Developmental disabilities represent alterations in the typical developmental sequence in one or more of three areas: motor, cognitive, and neurobehavior (Figure 54-1). “Motor” includes gross motor, fine motor, and visuomotor coordination. “Cognitive” includes central processing, problem solving, and language. “Neurobehavior” refers to self-help, self-regulatory, and social skills. These developmental disabilities are characterized by delay, dissociation, and/or deviation from the norm (Capute & Accardo, 1996).

A developmental delay is a significant lag in meeting milestones; for example, motor delays may indicate cerebral palsy. Dissociation is a difference between the rate of development in two aspects of one area—for example, between expressive and receptive language in children who are deaf. When the sequence of development in one or more areas deviates sufficiently from the norm, the overall pattern that emerges over time represents a different developmental path. In children with autism, the development of language, social, and problem-solving skills is so skewed that the pattern of play behavior and peer interactions that emerges is very different from the norm.

Mental retardation is characterized by “subaverage intellectual functioning” along with limitations in two or more adaptive skills (e.g., academics, communication, ability to live on one’s own, social skills, leisure, and work.) Mental retardation is a distinctive feature of fragile X syndrome, Down syndrome, and fetal alcohol syndrome. The current definition of mental retardation reflects
a new approach that broadens the previous emphasis on IQ scores to include abilities and adaptive skills.

Learning disabilities are characterized by a discrepancy between ability as measured on intelligence tests and actual achievement. The most common learning disabilities involve language function and metacognitive abilities, such as memory and problem solving. It is estimated that 3% to 15% of all U.S. school children have a learning disability.