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84 Chapter 5 Disorders of Early Childhood
Etiology
Much of what is known about the etiology of disorders of
attachment is based on what we know about the development
of insecure patterns in typical and at-risk children. According
to Zeanah and Smyke (2009, p. 421), “[t]he propensity for
human infants to form selective attachments is believed to
be so strong that only in highly unusual and maladaptive
caregiving environments do attachments fail to develop. For
infants raised in species-at ypical rearing conditions, however,
seriously disturbed and developmentally inappropriate ways
of relating may evolve. Examples of atypical environments
include institutions (i.e., orphanages), frequent changes of
caregivers (as sometimes happens in foster care), neglectful
or abusive caregivers, or being raised by insensitive or
unresponsive caregivers.”
For both RAD and DSED, the role of caregiving (i.e.,
caregivers and the caregiving environment) is primary.
Neglectful and abusive caregiving leads to insecurity and
disorders of attachment, with more neglect and more abuse
associated with increasingly negative outcomes. Extremely
adverse caregiving environments include institutions
and problematic foster care and home settings that are
characterized by chronic maltreatment and domestic
violence (Zeanah & Gleason, 2015). “Institutional rearing
due to its regimented nature, high child-to-caregiver ratios,
multiple shifts, and frequent changes of caregivers almost
inevitably deprives children of reciprocal interactions with
stable caregivers” (Steele & Steele, 2014, p. 363).
Distinctions between adverse caregiving characterized
by trauma (such as maltreatment) and adverse caregiving
characterized by deprivation (such as neglect) provide
important information (Guyon-Harris et al., 2021). Young
children may experience exposure to “low deprivation/
low threat (e.g., safe and stimulating environments), high
deprivation/low threat (e.g., severe neglect and institutional
rearing), low deprivation/high threat (e.g., exposure to
violence and abuse), and high deprivation/high threat
(e.g., complex exposures)” (Guyon-Harris et al., 2021,
p. 88; McLaughlin et al., 2014). These different adverse
caregiving environments may lead to different disorders or
combinations of disorders over time.
Children with disorganized attachments are more likely
to develop DSED (Zeanah & Gleason, 2015). Disorganized
attachments are associated, as noted earlier in the chapter,
with frightening, frightened, and/or dissociative parenting
behaviors. They may also occur in parent-child pairs where
the parent experienced significant loss or trauma or as a
result of long or repeated separations from the caregiver.
Infant genetic predispositions and temperament dimensions
may also contribute to disorganized attachments (Granqvist
et al., 2017). With respect to genetic influences on children’s
disorders of attachment, results from various investigations
suggest increased differential susceptibility to poor
parenting (i.e., insensitivity and/or frightening or other
atypical behavior) (Drury et al., 2011; Zeanah & Gleason,
2015).
Remember, however, that not all children living in adverse
environments or experiencing problematic care develop
attachment disorders. We need to consider other risk factors
that help explain the most maladaptive pathways. Reviews
of parent factors that increase risk for attachment disorders
include personality and psychopathology, attachment
history, and other contextual variables. Mental illness in
parents has received a lot of attention. Maternal depression,
bipolar disorder, anxiety, substance abuse, and schizophrenia
have all been associated with greater frequency of insecurity
and attachment disorders in children. Neglectful and
abusive caregiving also may occur in the context of chronic
interparental conflict, hostility, and violence (Cummings &
Miller-Graff, 2015; Davies & Martin, 2013).
Assessment and Diagnosis
In contrast to much of the research-oriented assessment of
attachment in typical and at-risk samples of young children,
the clinical assessment of disorders of attachment involves
more naturalistic data collection. Home visits or assessments
in home-like settings are preferable, and in some cases may be
necessary. Parent reports and observations are an important
source of information (Zeanah & Gleason, 2015).
Perhaps the most important contributions to the
accurate assessment of disorders of attachment are
observations of the child in the everyday environment.
For reactive attachment disorder, clinical interpretations
of real-life caregiver–child interactions are essential for
understanding the dynamics of attachment (and the
absence of attachment behaviors). For disinhibited social
engagement disorder, observation of the child in multiple
social settings is essential. In the clinical cases presented
earlier in the chapter, direct observation of the children
contributed to making the correct diagnosis.
In terms of ass essments that identif y risk factors a ssociated
with early and later maladaptation, clinicians may choose
to include measures of irritability (Wakschlag et al., 2015).
To better design interventions, assessments of caregiver
history and functioning (focused on parent risk factors
that increase risk for attachment disorders) may also be
useful.
Although much of the research and clinical attention
currently paid to disorders of attachment is focused on
young children, many instances of these disorders are
identified and assessed in older children. With increasing
age, it becomes more important to develop a therapeutic
alliance with a child or adolescent to make an accurate
diagnosis and design an appropriate intervention. Older
children and adolescents often exhibit multiple problems,
including aggression, anxiety, and depression, with a
number of children meeting the diagnostic criteria for
several disorders. Some of these disorders have their
etiological roots in disorders of attachment, and others do
not. A comprehensive assessment—whether simple and
straightforward or messy and complicated—will always
keep the child in full view.
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Disorders of Attachment 85
Intervention
Within the f ramework of de velopmental psychopat hology,
it is both theoretically and practically easier to prevent
the development of disorders than it is to intervene
effectively once disorders are in place. Children, parents,
and mental health professionals, however, must deal with
real-life circumstances. And real life requires that we
design and validate therapeutic interventions for disorders
of attachment. Keep in mind as well that prevention
strategies and attachment-related interventions to
improve young child-caregiver relationships also serve
to decrease risks for later disorders of childhood and
adolescence.
Prevention strategies related to disorders of attachment
can be usefully categorized as universal measures for the
general population, selective measures for groups at aboveaverage risk, and indicated measures for groups with
specific risk factors that require more extensive help.
Examples of universal measures designed to promote
infant and parent well-being are infant and toddler
education programs delivered before and after the baby
is born.
Examples of selective measures to enhance child, parent,
and family well-being include those provided to caregivers
at high risk for maltreatment. The Attachment and
Biobehavioral Catc h-up (ABC) progra m is a brief inter vention
that targets three key behaviors: providing nurturant
care when children are distressed, following children’s leads
when they are not upset, and not exhibiting frightening
behavior. Caregiving coaches provide immediate feedback
to parents in therapy sessions. Young children whose
parents participated in the program displayed more secure
and more organized attachments (Dozier & Bernard,
2017).
Another example involves the early identification
of families where parents experienced their own lessthan-adequate care. Treatments are offered that disrupt
intergenerational cycles of abuse by providing education
and support for positive parenting (Granqvist et al.,
2017). In many of these prevention and intervention
approaches, it is important to recognize that the
parent-therapist alliance is critical for engagement
and good outcomes. Blaming parents, especially for
parenting behaviors that are not always intentional and
not always malicious, is counterproductive (Granqvist
et al., 2017).
With respect to therapeutic approaches for children
already diagnosed with reactive attachment disorder or
disinhibited social engagement disorder, meaningful
improvement depends on the duration and degree of
disorder, particular etiology, age of the child, and the
scope of environmental change. “The first priority of
treatment is to establish a safe and stable caregiving
environment with a warm and consistent caregiver,” with
the goals of enhancing adaptive behaviors and decreasing
maladaptive behaviors (Zeanah & Smyke, 2009, p. 429).
Indeed, with adoption or positive foster placements,
children with RAD display significant improvement;
symptoms diminish or disappear in sensitive caregiving
environments. The symptoms of DSED are more
persistent, so children with that disorder require
additional treatment components beyond enhanced
caregiving (Zeanah & Gleason, 2015).
Attachment-informed interventions such as ChildParent Psychotherapy (CPP) have received a lot of empirical
support. CPP includes therapy sessions with caregivers and
children focused on protective caregiving and replacing
maladaptive beliefs that parents have about children with
more realistic and positive beliefs (Lieberman et al., 2015).
Video-feedback components and interventions provide very
specific information about what caregivers are doing well
and what they might do differently (Juffer et al., 2017).
Group-based attachment interventions have also received
empirical support. The group format provides additional
benefits such as decreasing families’ isolation and promoting
positive change (Murphy et al., 2015).
Other interventions are focused on increasing caregivers’
capacities and skills related to mentalizing, the ability to
understand the self and others in terms of feelings, thoughts,
needs, motives, and goals. Mentalizing interventions
support caregivers’ positive connections to young children.
Their strengthened appreciation of children’s inner states
and inner worlds improves sensitive caregiving and secure
base provision (Luyten et al., 2020).
Another perspective on promoting the availability,
consistency, and quality of caregiving involves levels
of adverse contexts and interventions (Humphreys
et al., 2021, refer to Figure 5.6). Interventions for
children without caregivers involve family placements.
Interventions for children with inconsistent care involve
addressing barriers to better care such as violence
prevention measures and treatments for parental
substance use or mental illness. Interventions for children
with ineffective care involve caregiver-focused treatments
such as attachment and behavioral catch-up and childparent psychotherapy.
It is absolutely critical to state that attachment
holding interventions have been “completely discredited
as dangerous, unethical, and importantly, also
ineffective” (Guyon-Harris et al., 2021, p. 91; Chaffin
et al., 2006).
Treatments also are provided to adolescents who were
maltreated as children. For adolescents in foster care,
the development of an attachment relationship with a
foster parent predicts fewer externalizing problems. It is
encouraging that there is still “substantial potential for
maltreated children to change and develop subsequent
secure attachments in adolescence” (Joseph et al., 2014,
p. 67). Other clinical research confirms that hard-to-reach
adolescents are able to make important connections to
therapists using attachment-based strategies that support
their therapy goals (Bevington et al., 2015).
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86 Chapter 5 Disorders of Early Childhood
Key Terms
Temperament (68)
Reactivity (68)
Regulation (68)
Differential susceptibility (71)
Resistant (anxious/ambivalent) attachment (72)
Chapter Summary
●
The mental health and well-being of infants, toddlers,
and young children requires that we identify and
respond to patterns of distress and dysfunction in early
development.
●
Physiological systems, including the important sleep
system, undergo changes in the early years with
meaningful consequences for typical and atypical
development.
●
Temperament is best understood as dimensions or profiles
of activity, affectivity, and self-regulation. Temperament
is reliably related to later personality and contributes to
pathways of adaptation and maladaptation.
●
The development of a secure attachment relationship
between infant and caregiver is the critical task in the
first year of life. Secure attachment relationships are
the result of consistent, appropriate responsiveness by
the caregiver to the infant’s physical, emotional, and
social needs.
●
Insecure attachments—including resistant, avoidant,
and disorganized attachments—reflect inconsistent,
ineffective, and/or inappropriate caregiving.
●
Attachment processes and caregiving environments
are associated with a wide range of physiological,
psychological, and social outcomes across development.
●
Problematic patterns of temperament and attachment
often reflect significant distress and dysfunction but do
not necessarily lead to a diagnosis. These early patterns
may be usefully understood as risk factors for ongoing
difficulties and later disorders.
Avoidant (anxious/avoidant) attachment (73)
Disorganized attachment (73)
Irritability (75)
Avoidant/restrictive food intake disorder (ARFID) (76)
Sleep–wake disorders (78)
Reactive attachment disorder (RAD) (80)
Disinhibited social engagement disorder (DSED) (80)
●
Irritability, involving negative mood and intense
dysregulation, helps explain some of the connections
between early patterns of distress and dysfunction and
later disorders.
●
Feeding di sorders represent an impa irment of efficient and
effective feeding—an especially salient developmental
task in infancy and early childhood. Multiple factors
contribute to feeding difficulties. Behavioral and
relationship interventions are effective in improving
outcomes.
●
The sleep-wake disorders most common in early
development are those that involve significant difficulties
falling or staying asleep. Multiple factors contribute
to sleep-wake disorders. As with feeding disorders,
behavioral and relationship interventions are effective in
improving sleep and sleep outcomes.
●
DSM-5-TR describes two kinds of attachment disorders:
reactive attachment disorder (RAD) and disinhibited
social engagement disorder (DSED).
●
Severely adverse caregiving environments, such as those
related to institutionalization, maltreatment, and/or neglect,
contribute to the development of disorders of attachment.
●
Interventions for disorders of attachment range from
universal measures for the general population to more
selective measures that target more specific risk factors
and high-risk groups.
●
There are several effective relationship-based treatments
for disorders of attachment, with a focus on providing
children with sensitive caregiving and positive parenting.
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6
Intellectual Developmental Disorder
and Learning Disorders
Chapter Outline
Developmental Tasks and Challenges Related
to Intelligence and Cognition 88
Components and Mechanisms of Intelligence
Cognitive and Intellectual Functioning across Development
Genes, the Brain, and the Environment
Measures of Intelligence
Intellectual Developmental Disorder 91
The Case of Katherine
Zigler’s Developmental Approach to Intellectual
Developmental Disorder
Genotypes and Neurobehavioral Phenotypes
Down Syndrome
Williams Syndrome
Fragile X Syndrome
Fetal Alcohol Spectrum Disorder
Etiology 95
Developmental Course 96
Language, Communication, Executive Function, and Learning
Socioemotional Functioning, Motivation, and Personality
Box 6.1 The Child in Context: Enhancing Success in
Inclusive Classrooms
Learning Objectives
Maladaptive Behavior and Comorbid Disorders
Adult Outcomes
The Role of the Family
Risk and Resilience
Assessment and Diagnosis 100
Assessment of Intellectual Functioning
Assessment of Adaptive Functioning
Other Assessment Concerns
Intervention 101
Genetic Screening and Prevention Strategies
Pharmacological Treatment
Psychological Treatment
Family Education and Support
Learning Disorders 103
The Case of Ethan
Developmental Course 105
Etiology 105
Assessment, Diagnosis, and Intervention 106
1. Summarize the major models of intelligence and its components.
2. Summarize the ways in which cognition and intelligence
develop over time.
3. Discuss the ways in which genetic, brain, and environmental
factors influence intelligence over time.
4. Describe the ways in which intelligence has been measured
over the past century.
5. Discuss the constructs of intellectual functioning, adaptive
functioning, and quality of life in relation to intellectual
developmental disorder.
6. Explain Zigler’s developmental approach and its impact on the
current understanding of intellectual developmental disorder.
7. Compare and contrast two types of intellectual
developmental disorder with specific etiologies.
8. Summarize various family influences on the development of
intellectual developmental disorder.
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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
9. Compare and contrast varied developmental pathways for youth
with intellectual developmental disorder, including information
about language and communication, socioemotional
functioning and relationships, and long-term outcomes.
10. Summarize the main assessment techniques for intellectual
developmental disorder.
11. Summarize approaches to prevention and intervention for
intellectual developmental disorder.
12. Explain the main findings related to cognitive models of
learning disorders.
13. Compare and contrast a positive developmental pathway
and a problematic developmental pathway for two youths
with learning disorders.
14. Summarize the assessment techniques and interventions for
learning disorders.
87
88 Chapter 6 Intellectual Developmental Disorder and Learning Disorders
Children with intellectual developmental disorder have
been the causes of bewilderment, the targets of ridicule and
institutionalization, and the focus of many adults’ love and
care. A ny historical perspective on intellectua l developmental
disorder must include the centuries of mistaken, harmful
beliefs and useless, sometimes cruel interventions. Historical
perspectives must also include the longstanding concern
and support for children with intellectual disabilities
displayed by parents, teachers, and medical and mental
health professionals. Contemporary, holistic approaches to
understanding intellectual developmental disorder and the
very diverse group of individuals who share that diagnosis
are the focus of this chapter.
Developmental Tasks and Challenges Related to Intelligence and Cognition
Theoretical models and empirical studies emphasize the
need to understand the complex construct of intelligence
and its contribution to typical and atypical development
across cultures and in a variety of settings (Pennington, 2015;
Sternberg, 2019). We know that cognitive and intellectual
development predicts academic, work, and health outcomes
across the lifespan. Intelligence is linked with school success
and educational achievement, job performance, and better
health and a longer life (Deary, 2021).
The following summaries are organized around several
key issues: (1) What are the underlying components and
mechanisms of intelligence? (2) How does cognitive and
intellectual development unfold over time? (3) What are
the roles of genes, brain structure and function, and the
environment in the development of intelligence? (4) How
do we measure intelligence?
Components and Mechanisms
of Intelligence
The most basic question involves the nature of intelligence.
This definition has been used by many researchers for a long
time: “[Intelligence] ... involves the ability to reason, plan,
solve problems, think abstractly, comprehend complex ideas,
learn quickly and learn from experience. It is not merely book
learning, a narrow academic skill, or test-taking smar ts. Rather
it reflects a broader and deeper capability for comprehending
our surroundings—‘catching on,’ ‘making sense’ of things, or
‘figuring out’ what to do” (Gottfredson, 1997, p. 13).
Researchers agree that intelligence involves the
performance of mental tasks, including adaptation to one’s
environment, learning, reasoning, problem solving, and
planning. Many models of intelligence emphasize the verbal
and mathematical abilities or skills related to academic,
educational, and occupational outcomes. Other descriptions
of intellectual ability include specific skills and talents
such as aesthetic (e.g., musical), mechanical, social, and
nature-based intelligences (Gardner, 2018). Motivational
factors such as growth mindsets, curiosity, and effort also
contribute to intellectual functioning (Dweck & Yeager,
2021; Kovas et al., 2015).
The Cattell-Horn-Carroll (CHC) model of intelligence
is the most influential model. The CHC model integrates
two theories of intelligence: the Horn and Cattell FluidCrystallized theory and Carroll’s hierarchical theory. The
Fluid-Crystallized theory differentiates between fluid
intelligence, the ability to reason and solve problems in new
situations, a nd crystallized intelligence, the ski lls and k nowledge
acquired through education and experience. Carroll’s theory
describes a multi-level approach with a general ability
factor, g, accounting for most of the variance in intellectual
functioning. Carroll also describes a level with eight broad
abilities, including fluid intelligence, crystallized intelligence,
general memory and learning, processing speed, auditory
processing, visual perception, retrieval ability, and decision
speed. There are approximately 70 more narrow abilities at
a third level of functioning (McGill & Dombrowski, 2019;
McGrew, 2009). The CHC model is especially important
because it influences the development and revision of many
tests designed to assess intelligence and cognitive ability in
schools and clinical contexts (McGill & Dombrowski, 2019).
Another perspective on intelligence contrasts general
intelligence, typically assessed by tests focused on cognitive
tasks, with adaptive intelligence, intelligence that is used
in the context of biological adaptation to the environment
(Sternberg, 2019). Adaptat ion to environments includes f itt ing
into environments, shaping environments to fit oneself, and
selecting new environments. Adaptive intelligence includes
practical, creative, and wisdom-based skills. There are, of
course, overlapping intellectual processes across general
and adaptive intelligences. These include “recognizing the
existence of a problem, defining the nature of a problem,
mentally representing the problem, formulating a strategy to
solve the problem, monitoring the strategy’s effectiveness … ,
and evaluating the effectiveness of the strategy after problem
solution” (Sternberg, 2019, p. 26). Adaptive intelligence may
be assessed in individuals, in groups, or in species. Multiple
factors inf luence the ways in which these general and adaptive
intelligences are used in different settings and valued by
different groups and cultures (Nisbett, 2019).
Cognitive and Intellectual Functioning
across Development
To understand the pathways displayed by children with
intellectual developmental disorder and the ways in which
learning is accomplished for typically developing children
and compromised for children with learning disorders, we
must examine both cognitive development (general agerelated trends) and intellectual development (individual
differences observed across children at all ages). With respect
to cognitive development, we need to pay attention to the
components and processes of cognition (e.g., perception,
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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Developmental Tasks and Challenges Related to Intelligence and Cognition 89
Age (years)
18
Proportion of variance in cognition
Genes
attention, memory, concept formation, and mental rules
and representations). As described in Chapter 2, research on
cognitive development focuses on the dynamic interaction
of tasks, contexts, and emotional states that influence
cognition to explain the how and why of children’s thinking
and learning. Models of cognition emphasize evolutionary
contexts, behavioral genetics, and epigenetics and both
qualitative and quantitative change across development
(Bjorklund, 2018).
There is general agreement that typically developing
children display steady, linear progress in cognitive
achievements, with occasional reorganizations or
qualitatively distinct developmental leaps. For example,
children learn and remember more information as they
age, but they also become faster and more efficient at
manipulating that information. The pace of progress is
greater through the preschool and elementary school years
and slows somewhat during adolescence.
With respect to intellectual development, there is an
ongoing emergence of intellectual functioning as well as
patterns of strengths and weaknesses in both components
and mechanisms (Bjorklund, 2018). Components and
mechanisms include factors such as reasoning, problem
solving, and learning. Individual differences, with some
children displaying higher levels of intelligence and other
children displaying lower levels, appear relatively stable from
four or five years of age through adulthood, with growth,
change, and decline observed throughout the lifespan
(Deary et al., 2021).
Genes, the Brain, and the Environment
Both heredity and the environment contribute to children’s
cognitive and intellectual development. Numerous genes
are involved in the development and stability of complex
psychological traits such as intelligence. The contribution
of any single genetic variant is relatively tiny. The genetic
variants associated with brain structure and function appear
to influence general intellectual abilities rather than specific
ones, with links to neurogenesis (i.e., the creation of new
neurons), neuron differentiation, and synaptic processes.
Imaging technology provides compelling evidence of
differences in brain volume, grey matter, white matter, and
connectivity over time (Bathelt et al., 2019; Deary et al.,
2021; Plomin & Von Stumm, 2018).
Genetic effects on intelligence increase w ith a ge. Examples
of gene by environment by time (G × E × T) processes
illustrate these effects. As children age, they are increasingly
able to select environments and seek out experiences that
align with their genetic predispositions. Children with
above average abilities, for example, may choose more
challenging books to read or spend more time taking apart
electronics to understand how they work. Children are
also directed to specific environments and experiences by
adults. Parents may sign up tech-savvy children for science
camps and teachers may encourage language-loving kids
to participate in extracurricular activities such as debate or
theater. Early genetic influences on cognitive abilities, then,
become amplified (or magnified) over time (Tucker-Drob
et al., 2013; refer to Figure 6.1).
The increasing impact of genes on the variance and
stability of intelligence is clear when it is compared to the
impact of genes on personality over time (Briley & TuckerDrob, 2017; refer to Figure 6.2). It is also important to
note the decreasing influence of shared environments over
time for intelligence and the absent influence of shared
environments on personality. These data suggest that it
is essential to consider each child’s unique experiences in
family and environmental contexts.
Genetic effects also contribute to individual differences
in motivational factors such as intellectual interest.
Intellectual interest differentially predicts knowledge and
academic achievement for children in high-SES and lowSES circumstances (Briley & Tucker-Drob, 2017, p. 59).
That is, children who are more curious seek out experiences
that support learning and even more curiosity but only if
they are in settings such as homes with books and creative
toys, high-quality daycares, and well-resourced classrooms
where these learning experiences are available and where
adults can direct and support them. When we explore the
interaction of genes and environments for intelligence and
motivational factors, we understand better how children
who experience the many disadvantages of poverty may not
be able to develop their full or real intellectual potential.
In addition to SES, the child’s immediate and larger
environments also have considerable impact. Prenatal
and postnatal environments are very important. Maternal
drug or alcohol use or exposure to toxins negatively affects
Figure 6.1 Genetic and environmental
influences on cognition across development
Family environment
1.0
0.8
0.6
0.4
0.2
0.0
0246810 12 14 16
Source: Tucker-Drob et al. (2013). Genetic and Environmental Influences
on Cognition Across Development and Context.
Unique environment
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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
90 Chapter 6 Intellectual Developmental Disorder and Learning Disorders
Age (years)
Variance in Cognitive Ability
Proportion of variance in cognitive ability
Age (years)
Variance in Personality
90
Figure 6.2 Proportion of variation in cognitive ability and personality attributable to genes,
shared environment, and nonshared environments
1.0
Genes
Shared environment
0.8
0.6
0.4
0.2
0.0
Source: Briley & Tucker-Drob (2017). Comparing the developmental genetics of cognition and personality over the lifespan.
10 20 30 40 50 60 70 80 90
Nonshared environment
intellectual and cognitive abilities. Parental factors such as
education, interest in academics, and beliefs about children’s
intelligence have all been associated with more positive
intellectual outcomes (Dweck & Yeager, 2021; Nisbett
et al., 2012). Sociocultural influences on curricular content,
teaching practices, and classroom settings also contribute
1.0
0.8
0.6
0.4
0.2
Proportion of variance in personality
0.0
10 20 30 40 50 60 70 80
scores observed over many decades (Flynn, 1987, 2007). With
data on IQ trends in 30 nations, researchers suggest that societal
development and modernization led to intellectual gains. Better
nutrition, reductions in exposure to environmental toxins,
better health, and better schooling continue to contribute to
meaningful gains in intelligence (Giangrande et al., 2022).
to differences in academic pathways and achievement (Ellis
et al., 2017; Sternberg, 2019).
One last point about environmental factors, in cultural
and global context: Our understanding of children’s (and
adults’) intelligence across countries and continents requires
consideration of the “Flynn effect,” the gradual increase in IQ
Measures of Intelligence
The measurement of intelligence across the range of
cognitive abilities has been the source of many scientific
controversies and ethical issues. Intelligence and IQ testing
were tragically linked to the eugenics movement in the early
20th century. Intelligence and IQ testing were also the focus
of many vehement nature-nurture assertions, particularly
those connected to innate differences and racial and cultural
bias. The use of biased intellectual and ability tests to track
students problematically and unfairly into academic and
non-academic pathways reflects another misuse of theory
and research on intelligence (Deary et al., 2021).
The history of intelligence testing of youth in the US
provides another perspective on the goals and consequences
of testing (Kranzler et al., 2016). Between the late 1800s and
the early 1900s, school reforms in teaching and curricula were
required to meet the needs of an increasingly large and diverse
group of children. By the mid-1920s, group intelligence tests
were widely used to sort students by ability. Approximately
istock.com/SDI Productions
50 years later in 1975, the Education for all Handicapped
Curricular content, teaching practices, and classroom settings
influence academic pathways and achievement.
Children Act was passed by the US Congress and reauthorized
in 2004 as the Individuals with Disabilities Education Act
Genes
Nonshared environment
(shared environment = 0)
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Intellectual Developmental Disorder 91
02
IQ
Org
(IDEA). The law mandates free and appropriate education
and services for youth with disabilities. Although the law
provides guidelines for the use of intelligence tests, there is
wide leeway for state implementation (Kranzler et al., 2016).
Individual intelligence tests are used to identify
intellectual developmental disorder, learning disorders, and
giftedness. The most frequently used measures of intellectual
and cognitive ability are the Wechsler Intelligence Scale
for Children, the Stanford-Binet Intelligence Scale, the
Woodcock-Johnson Tests of Cognitive Abilities, and the
Kaufman Assessment Battery for Children. The CHC
model of intelligence is increasingly used to guide test
development and revision. School psychologists, child
clinical psychologists, and other licensed specialists are
trained to do these assessments and interpret the results
(Kranzler et al., 2016; McGill & Dombowski, 2019).
There are many ways to score and interpret intelligence
and ability tests and almost as many theoretical and
psychometric concerns (Beaujean & Benson, 2019). These
concerns include the lack of a strong evidence base for many
of the subtests and scores on widely used tests. These concerns
also raise questions about some of the interpretations and
recommendations made by test administrators. Meaningful
decisions about classroom assignments, special education
services, and short- and long-term educational achievement
require the best possible assessments.
Intellectual Developmental Disorder
Table 6.1 Intellectual Developmental Disorder:
Summary of DSM-5-TR Diagnostic Criteria
A. Deficits in intellectual functioning including
general reasoning, problem solving, abstract
thinking, and academic learning, in comparison to
age-, gender-, and socioculturally-matched peers.
B. Deficits in adaptive functioning resulting in
inability to meet age-normed developmental
expectations in areas such as personal
independence, communication, and social
behavior. Ongoing support needed in one or more
activities of daily living across multiple settings,
including home, school, work, and community.
C. The onset is during the developmental period
and is based on clinical assessment and testing
of intellectual functions, neuropsychological
tests, and tests of adaptive functioning.
Although both the DSM-5-TR and AAIDD
conceptualizations of intellectual developmental disorder
recognize the interdependent nature of intellectual
and adaptive functioning as well as multiple etiologies
and outcomes, the AAIDD emphasizes a more holistic
perspective. In this view, IDD is not a physical or mental
disorder but rather a developmental disability that involves
Intellectual developmental disorder (previously known
as intellectual disability) involves deficits in intellectual
functioning and deficits in adaptive functioning, both of
which emerge early in development (American Association
on Intellectual and Developmental Disabilities (AAIDD),
2021; American Psychiatric Association, DSM-5-TR, 2022)
(refer to Table 6.1). Deficits in intellectual functioning are
evaluated with respect to the range and distribution of
intelligence (IQ) scores in typically developing individuals
(refer to Figure 6.3).
One of the most important distinctions related to the
clinical presentation of intellectual developmental disorder
is level of severity. Mild, moderate, severe, and profound levels
of severity indicate the degree of impairment in adaptive
functioning. According to the American Association on
Intellectual and Developmental Disabilities (AAIDD)
and DSM-5-TR, adaptive functioning refers to how well
an individual negotiates everyday tasks and challenges in
conceptual, social, and practical domains. Some children
with below average adaptive functioning exhibit significant
problems with basic activities of daily living such as
getting dressed and maintaining hygiene; others do well
with basic tasks but struggle with more complex activities,
such as performing household chores or managing school
responsibilities.
Figure 6.3 Bimodal distribution of IQ scores
Familial
anic
03570100 15
Source: Zigler & Hodapp (1986). Understanding Mental Retardation.
Reprinted with the permission of Cambridge University Press.
00
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92 Chapter 6 Intellectual Developmental Disorder and Learning Disorders
significant limitations both in intellectual functioning
and in adaptive behavior leading to impaired conceptual,
social, and practical skills. Conceptual skills include
language and literacy; number, money, and time concepts;
and self-direction. Social skills include interpersonal skills,
gullibility and naivete, the ability to follow rules, and the
ability to avoid being victimized. Practical skills include
personal care, schedules and routines, safety, and travel
and transportation. Each area of dysfunction includes a
corresponding description of the support necessary for
maximizing the individual’s well-being: intermittent,
limited, extensive, or pervasive support.
Rather than emphasizing the degree of deficit, the
AAIDD emphasizes the possibility of adaptation.
Whether the definition of intellectual developmental
disorder emphasizes deficits or supports, it is important
to acknowledge the impact that the actual name of
a disorder or a disability has on individuals who are
diagnosed, on family members, and on society. Labels
and terms that are clear and unbiased and “that optimize
outcomes rather than interfere with them” are the labels
and terms that should be used to enhance communication
and decrease stigma and discrimination (Woods et al.,
2019, p. 693).
Decades of work on the quality of life construct
exemplify the integration of person-by-environment
ecological models and the support-based approach to IDD
(Schalock & Alonso, 2022). Quality of life (QOL) includes
three factors: independence, social participation, and wellbeing. Independence reflects an individual’s personal
development and self-determination. Social participation
reflects an individual’s relationships and inclusion. Wellbeing includes emotional, physical, and material outcomes
(refer to Table 6.2). An individual’s system of supports
should address all these aspects of adaptation.
Table 6.2 The Quality of Life (QOL) Framework
Factor Domain
Independence Personal Development
Self-determination
Social Participation Interpersonal Relationships
Social Inclusion
Human and Legal Rights
Well-Being Emotional Well-Being
Physical Well-Being
Material Well-Being
Adapted from: Schalock and Alonso (2013). The Impact of the Quality of
Life Concept on the Field of Intellectual Disability.
The Case of Katherine
Katherine is an 8-year-old girl, the fourth of seven brothers
and sisters, but her mother, Mary, always refers to her as
“my baby, because she never fusses.” Katherine and her
family live with her grandmother in the small threebedroom apartment where Mary grew up. Mary dropped
out of high school when she became pregnant with her
first baby at age 15. Katherine’s grandmother cleans
houses for a living, and Mary cares for the children, who
range from 2 to 14 years of age. Katherine’s father, Philip,
is a food services worker at the local hospital. He visits the
children infrequently.
When Katherine neared the end of first grade, her
mother was surprised to hear her teacher’s concern
that she wasn’t making adequate progress at school.
Katherine’s three older brothers had been a handful, with
each of them experiencing discipline problems ahead of
Katherine in the same public school. Mary had noticed
that Katherine seemed to lag a little behind her brothers
in learning to walk and talk, but she just assumed that she
would eventually catch up. Mary didn’t usually make it to
parent nights at school, but she had heard no bad reports
on Katherine from the kindergarten teacher, and she was
always pleased by how Katherine played so well with her
younger sisters. But the teacher told Mary that Katherine
wasn’t making progress in letter and word recognition,
had difficulties following directions, and seemed to be
getting more and more anxious and disconnected from
the other children as the year went on. It didn’t help that
some of the other children had started to tease Katherine
about her reading struggles.
The school psychologist’s assessment of Katherine
revealed that she had an IQ of 65 and adaptive skill
deficits in the sensorimotor, communication, and selfhelp areas. Katherine’s functioning in each of those areas
was more than two standard deviations below the norm
for her peers, which led to her diagnosis of intellectual
developmental disorder of mild severity.
An Indiv idualize d Education Plan (IEP) wa s developed
in which Katherine remains in the regular classroom
for about half the day with the support of a teacher’s
aide to guide her work more closely. She also leaves
the classroom periodically to participate in specialized
classes dedicated to more intensive work on her reading,
fine motor, and auditory processing abilities. The IEP
contains very specific goals in each skill area along with
a timetable for evaluating Katherine’s progress toward
each of the goals several times a year. Like any child,
Katherine has individual strengths and weaknesses in
different areas, and the learning goals are continually
readjusted over time to reflect progress or the need to
reinforce certain skills. Katherine’s classroom teacher
has also adopted a curriculum unit that addresses
disability stereotyping and helps the other children in
the class to both understand and be more supportive of
Katherine.
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Intellectual Developmental Disorder 93
The school psychologist met with Mary to help her
better understand the nature of Katherine’s disability and
her future expectations. She explained that Katherine’s
development in many ways follows the same sequence
and growth pattern as other children but progresses more
slowly and will not continue as far in terms of her ability
to think abstractly and process complex information. As
she matures, her caregivers will need to pay increasing
attention to the level of support that Katherine requires,
in line with the standards established by the AAIDD. It is
likely that Katherine’s necessary support level as she moves
into adulthood will fall somewhere between intermittent
(e.g., as needed, such as following a job loss or health crisis)
and limited (e.g., consistent support in areas like vocational
training and housing assistance that varies in intensity).
Taking into account the various definitions of intellectual
developmental disorder and the difficulties associated
with accurate calculations, epidemiological estimates of
the prevalence of IDD range between 1% and 3% of the
population (Maulik et al., 2011; Reichenbert et al., 2016;
Zablotsky et al., 2019). Most individuals (85%) with
IDD are diagnosed with mild levels of severity, requiring
intermittent support (as described in the case of Katherine).
Approximately 10% are diagnosed with moderate levels,
requiring limited support; 3% to 4% with severe levels,
requiring extensive support; and 1% to 2% with profound
levels, requiring pervasive support. IDD is observed much
more frequently in boys (Zablotsky et al., 2019).
Zigler’s Developmental Approach to
Intellectual Developmental Disorder
Several of the most important and affirming proposals
about children with intellectual developmental disorder
were put forth by Edward Zigler (1969, 1971). Zigler
described two groups of children. The first group included
children with mild forms of intellectual disability, reflecting
the low end of the normal distribution of intelligence in the
general population (refer to Figure 6.3). Because this type of
intellectual disability appeared to run in families, it was (and
still is) often called familial (or cultural familial) intellectual
developmental disorder. The second group included children
with more severe forms of intellectual disability, usually the
result of genetic disorders.
Zigler’s developmental approach asserted that most
children with IDD (i.e., children with mild forms of
disability) display developmental pathways that are like
children without IDD. Although delayed in their mastery
of most motor, cognitive, emotional, and social tasks, and
stopping short of the eventual achievements of their typically
developing peers, children with IDD exhibit the same kinds
of sequences and coherent growth that are characteristic of
most children. That is, children with IDD develop slowly,
but in organized ways.
Broadening his concern beyond deficits and dysfunctions,
Zigler insisted on a holistic perspective, the critical need to
understand patterns of strengths and weaknesses, and the
motivations and personalities of children with intellectual
developmental disorder (also refer to Cicchetti & PoggeHesse, 1982). Zigler also emphasized the social deprivations
and stressors such as frequent failure experienced by
many children with IDD that influenced developmental
outcomes. The developmental approach of Zigler has
inspired decades of research and clinical work (Burack
et al., 2021; Hodapp, 2021).
Genotypes and Neurobehavioral
Phenotypes
A lot of research has focused on identifying and
understanding children with intellectual developmental
disorder by grouping them according to etiology. Attention
is often focused on various genotypes—the underlying
genetic variants—associated with IDD. As described in
Chapter 2, research on genetic and epigenetic factors has
increased exponentially, with much of the work focused on
neurodevelopmental disorders, including IDD (Pennington,
2015; Plomin & Deary, 2015). These genetic syndromes are
medical diagnoses rather than psychiatric or psychological
categories. The genotype assumption is that different
etiological explanations correspond to differences in specific
dysfunction and disability. Hundreds of individual genetic
variants (e.g., mutations, duplications, deletions) and major
chromosome abnormalities are linked with specific forms
of IDD. Most individuals with these identifiable genetic
etiologies display more severe forms of disorder. Research
on genetic disorders and IDD has largely focused on Down
syndrome, Williams syndrome, and Fragile X syndrome
(Hodapp, 2021).
The related construct of neurobehavioral phenotypes
emphasizes the likelihood that a child will display a
particular pattern of difficulties given a particular genetic
etiology. In other words, most children—but not all
children—with a particular genetic background will
display similarities related to physical characteristics,
neurophysiological processes, cognitive and linguistic
profiles, perceptual skills and deficits, socioemotional
functioning, and overall outcomes. One example of a
distinctive neurobehavioral phenotype is the extreme
eating behaviors observed in individuals with PraderWilli syndrome (and not in other individuals with other
genetically influenced disorders). Another example of a
phenotype is the neurobehavioral pattern displayed by
children who experience prenatal alcohol exposure. This
phenotype is associated with an environmental rather than
genetic cause.
Genotype-phenotype research goals include the descriptions
of coherent and organized patterns of deficits and dysfunction
observed in individuals diagnosed with intellectual
developmental disorder and other neurodevelopmental
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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.