With the advent of the Binet test in the early 20th century, professionals were provided with a way of quantifying intelligence and defining the condition subsequently known as mental retardation. Later, the American Association on Mental Retardation (AAMR) assumed a leading role in defining mental retardation for professional audiences. The AAMR definition was updated frequently in response to changes in the way that mental retardation was conceptualized by those in the field. As of the early 2000s AAMR definition states: “Mental retardation is a disability characterized by significant limitations both in intellectual functioning and in adaptive behavior as expressed in conceptual, social, and practical adaptive skills. This disability originates before age 18” (American Association on Mental Retardation, 2002). Examiners use standardized tests to assess intellectual and adaptive behavior functioning. As a part of the standardization process for these measures, normative groups are used to determine age based deviation scores that have a mean of 100 and, usually, a standard deviation of 15 points. Significant limitations are present when these scores are more than two standard deviations below the mean (i.e., a score of 70–75 allowing for the standard error of measurement for the specific assessment instrument used).
The AAMR definitions have typically been incorporated into current versions of other diagnostic systems. For example, the language of the 1992 AAMR definition is clearly evident in the Diagnostic and Statistical Manual of Mental Disorders–IV TR (APA, 2000). In contrast, state educational agencies vary considerably in which definition of mental retardation is used to establish eligibility guidelines. A survey of state agencies conducted by Denning, Chamberlain, and Polloway (2000) revealed that the 1983 AAMR definition of mental retardation was being used in 86 percent of the states in either verbatim or an adapted version and that only 7.9 percent of the states had incorporated the 1992 AAMR definition in an adapted or verbatim format. Moreover, 5.9 percent of the states used alternative definitions. The reasons for these differences in definition were not readily apparent from the published report.
In the early 2000s, the term mental retardation is rapidly falling into disfavor among professionals, families, and self-advocates. There is considerable pressure to change the term to something that is perceived as less stigmatizing, such as intellectual disability. Intellectual disability is the term that is currently used in many other English speaking countries, and, perhaps for that reason, this term was chosen by the American Association on Mental Retardation as a replacement in its organization name. The American Association on Intellectual and Developmental Disabilities is in concert with other prominent organizations such as the International Association for the Scientific Study of Intellectual Disabilities and the President's Committee for People with Intellectual Disabilities. Although there is increasing momentum for widespread change in terminology, the term mental retardation remains imbedded in public policy. For example, a diagnosis of mental retardation is typically required to establish eligibility for state and federal disability programs such as the Individuals with Disabilities Education Improvement Act of 2004, Social Security Disability Insurance, and the Medicaid Home and Community Based Waiver. Schalock, Luckasson, and Shogren have argued that “intellectual disability covers the same population of individuals who were diagnosed previously with mental retardation in number, kind, level, type and duration of the disability, and the need of people with this disability for individualized services and supports” (2007, p. 120). Although it is relatively easy for a professional association to adopt a change in terminology, as of 2007 it is expected to be some time before other associations and governmental entities would follow suit no matter how much the change is needed.
Contemporary definitions of mental retardation require assessment of general intellectual functioning and adaptive behavior to determine a diagnosis. General intellectual functioning is measured by an individually administered, standardized intelligence test. Measures appropriate for school age children include the Wechsler Preschool and Primary Scale of Intelligence (3rd ed.), the Differential Ability Scales-II, the Wechsler Intelligence Scale for Children (4th ed.), Kaufman Assessment Battery for Children-II, and Stanford-Binet (5th ed.). Test selection is based on the chronological age of the child and the child's general level of functioning as well as the test's ability to clearly differentiate among children who perform at the lower end of a particular test. Given the likelihood that a child with mental retardation may also have sensory impairment or physical disability or be nonverbal, assessments have to be highly individualized and require the use of specialized measures designed for these populations. For example, intelligence tests appropriate for nonverbal or hearing impaired students are the Test of Nonverbal Intelligence-3 and the Leiter International Performance Scale (Rev.). In general, intellectual assessments for children with mental retardation require an examiner with considerable skill and experience in the assessment of children with special needs (Sattler & Hoge, 2006).
Adaptive behavior is typically assessed by informant report given the need for information about typical behavior that would go beyond that observed in a formal testing situation. Informants can include parents, teachers, or some other adult with considerable knowledge of the child's daily functioning. Measures of adaptive behavior assess personal and social competence in meeting common life demands as determined by the child's chronological age as well as the child's cultural background. Examples of areas assessed by these measures include: communication and language skills, social and interpersonal skills, gross and fine motor skills, and degree of independence in daily living skills. There are several well standardized measures available as of 2007, including the Adaptive Behavior Assessment Sys-tem-II, Scales of Independent Behavior (Rev.) and the Vineland Adaptive Behavior Scales-II. These instruments vary in their coverage, but all assess skills and abilities consistent with the conceptual, social, and practical dimensions of adaptive behavior in the 2002 AAMR definition as well as the specific adaptive skill areas delineated in the DSM-IV TR (2000) (i.e. communication, self-care, home living, social skills, community use, self-direction, health and safety, functional academics, leisure skills, and work skills—for adults only).
Children with mental retardation are typically identified because they do not keep pace with developmental expectations in cognitive, language, social, and motor functioning. Typically, significant developmental delays in early childhood are predictive of poor academic functioning in childhood, as compared with same-age peers. Considerable study has been directed toward identifying the cognitive difficulties associated with mental retardation. Most of this work was conducted using experimental designs based on the deficit model of mental retardation. That is, comparisons were made between children with mental retardation and their same chronological age peers. Using this framework, nearly every cognitive process studied revealed dramatic differences between the two groups. The areas of study included attention, working memory, perceptual organizational skills, verbal problem solving, visual-spatial problem solving, vocabulary, language and abstract reasoning, among others. Subsequent studies have adopted a developmental perspective, in which the functioning of children with mental retardation is compared with typically developing children of comparable developmental level. Although some differences remain, it is clear that children with mental retardation generally follow the same developmental pathways as their typically developing peers but at a slower rate and do not ultimately attain as high a level.
Similarly, slower progress in attaining independence in meeting common life demands, or adaptive behavior, characterize children with mental retardation. It is a matter of some debate as to whether the observed deficits in adaptive behavior are a function of deficits in intellectual functioning. In fact, empirical studies indicate a high degree of correlation between measures of intelligence and adaptive behavior suggesting that they are not entirely independent entities. Moreover, some authors suggest that there are unique aspects of adaptive functioning that are not tapped by existing measures. These attributes include social intelligence, social competence, vulnerability, gullibility, and credulity. Greenspan (1999) argues that deficits in these areas contribute to the victimization of children with mental retardation as well as social and economic exploitation.
Throughout the 20th century, people realized that there are demonstrable and clinically relevant differences among people with mental retardation. Traditionally this differentiation was based on level of functioning. The terms mild, moderate, severe, and profound are in the early 2000s used in DSM–IV TR to designate levels of mental retardation that correspond to standard deviation units below the mean. Mild mental retardation is defined as between two and three standard deviations below the mean, moderate mental retardation is between three and four and so on. These categories have endured because there are clear differences among the levels in both cognitive performance and adaptive functioning. A similar subgroup classification system, using different terminology (i.e., educable, trainable, severe/profound), is still employed by some state education departments (Denning et al., 2000).
In 1992 the American Association on Mental Retardation published a revision of its classification manual that represented a paradigm shift for the field. In this system, reliance on a deficit oriented approach (i.e., mild, moderate, severe, and profound) was supplanted by a supports-based approach to describing the individual needs of persons with mental retardation. By so doing the severity level descriptions were abandoned and a diagnosis of mental retardation was based solely on IQ and adaptive functioning scores below 70 to 75. The new classification system required description of the degree of support needed to maximize a person's performance across a variety of functioning areas. Support was defined in terms of intensity and duration and categorized as intermittent, limited, extensive, and pervasive. Support needs were designated for each area of functioning— recognizing that an individual may require more intensive supports in some areas as contrasted with others. Accordingly, a person might require extensive supports in academic activities and intermittent support in self-care activities. Ultimately this information could inform intervention planning and enhance the person's overall functioning level. The AAMR (later AAIDD) published a Supports Intensity Scale for use with adults, with a children's version of the Supports Intensity Scale expected to follow.
A emphasis within the field as of 2007 is to focus on etiology in describing subgroups of children with mental retardation. For example, research aimed at defining the behavioral characteristics, or phenotypes, of various genetic disorders is moving ahead at an accelerated rate. Although a great deal of research has been focused on Fragile x, Angel-man, Prader-Willi, Smith Magenis, and Williams syndromes, much was also published on Down syndrome. Studies of specific genetic disorders have yielded information regarding cognition, language and communication, visual-spatial skills, social development, and maladaptive behavior that has implications for educational professionals (Fidler, Hodapp, & Dykens, 2002).
Beginning with the Education for All Handicapped Children Act in 1975, the Individualized Education Plan has been the blueprint for educational services provided to children with mental retardation. This act established that all children, regardless of ability, were guaranteed a free and appropriate public education in the United States. The early 21st century version of this landmark legislation is known as the Individuals with Disabilities Education Improvement Act of 2004. A guiding principle of this legislation is that services should be provided in the least restrictive environment. That is, children with disabilities should receive educational services with their typically developing peers to the greatest degree possible. The goal for students with disabilities is inclusion within the general education setting. Inclusion means more than physical presence in the classroom or other education setting. Various practices are used to facilitate inclusion such as cooperative learning and peer tutoring experiences as well as instructional tools or strategies that enhance the salience of the academic content. Generally speaking, children with needs for extensive or pervasive supports spend the majority of their day in self-contained educational settings while children with less intense support needs may spend the majority of their day in a general education class with special education teacher services.
Early 2000s legislation such as the No Child Left Behind Act has reinforced the view that children with disabilities, including mental retardation, should graduate from public schools with basic or fundamental knowledge in mathematics, literacy, science and technology, practical skills sufficient to be self-supporting upon graduation, and problem-solving skills that foster lifelong learning. The success with which students with mental retardation achieve these skills varies considerably. For those who experience the greatest challenge with the general curriculum, efforts have yielded a functional curriculum that provides critical skills needed to participate in daily routines. These skills include independent living skills, communication, social skills, academic skills, and transition and community living skills. Support within the general education curriculum for children with mild mental retardation can be achieved in several different ways such as the use of accommodations that provide equal access to learning, curriculum modifications based on the child's current level of academic mastery, and adaptations of instructional methods to facilitate completion of assigned tasks.
Instructional procedures vary according to the needs of individual children. In general, children with mental retardation require explicit instruction if they are to succeed in school. Research has focused on a variety of methods to maximize instructional outcome and to promote generalization to real world settings. Examples of these methods include encouraging choice-making and self determination to enhance motivation to learn, teaching self-monitoring skills to encourage independence in completing academic tasks, and embedding instruction within activities to promote stimulus generalization and student motivation while distributing instructional trials over longer periods of time.
Children with mental retardation are likely also to have other deficits, such as cerebral palsy, seizure disorders, and sensory impairment (such as hearing and/or visual problems). In general, children with severe or profound mental retardation are at greater risk for these associated conditions as compared with children with mild or moderate mental retardation. Children with mental retardation are also at increased risk for health conditions that may affect their attendance at school as well as their participation in school activities. Finally, children with mental retardation are also at greater risk for speech problems. These difficulties can include difficulty with articulation as well as voice problems such as abnormal pitch or voice intensity.
Psychiatric diagnoses are more common among children with mental retardation as compared with their typically functioning peers. Epidemiological studies suggest that the risk may be as much as four times greater. For example, a study of 10,000 children aged 5 to 15 years in Great Britain revealed that 39 percent of children with mental retardation met DSM-IV and ICD-10 criteria for at least one psychiatric disorder as compared with 8.1 percent of children without mental retardation (Emerson, 2003). The reasons for this increased risk are not well known. Generally it is believed that the increased prevalence of sensory disorders, epilepsy, and brain damage associated with many specific etiologies play a role as does atypical developmental experience. It could well be that many children do not meet the criteria for a diagnosis of mental disorder but do manifest sub-threshold levels of particular symptoms that warrant intervention. The terms behavior problems or behavior disorders are often used to describe such cases.
The emphasis on studying behavioral phenotypes associated with particular etiologies has revealed co-occurring behavior problems and psychiatric disorders. These associations include attention-deficit hyperactivity disorder in fetal alcohol syndrome, anxiety in Williams syndrome, oppositional and defiant behavior in Smith-Magenis and Down syndromes, and self-injury in Lesch-Nyhan, Prader-Willi, Smith-Magenis, and Fragile x syndromes. Moreover, epidemiological studies indicate that as many as 75 percent of children with autism also have mental retardation. These children can be particularly challenging in the school setting when they exhibit property destruction, physical aggression, self-injury, and tantrums.
See also:Special Education
American Association on Mental Retardation. (2002). Mental retardation: Definition, classification, and systems of supports (10th ed.). Washington, DC: Author.
American Psychiatric Association. (2000). Diagnostic and statistical manual of mental disorders. 4th ed. Washington, DC: Author.
Denning, C. B., Chamberlain, J. A., & Polloway, E. A. (2000). An evaluation of state guidelines for mental retardation: Focus on definition and classification practices. Education and Training in Mental Retardation and Developmental Disabilities 35, 226–232.
Emerson, E. (2003). Prevalence of psychiatric disorders in children and adolescents with and without intellectual disability. Journal of Intellectual Disability Research 47, 51–58.
Fidler, D. J., Hodapp, R. M., & Dykens, E. M. (2002). Behavioral phenotypes and special education: Parent report of educational issues for children with Down syndrome, Prader-Willi syndrome, and Williams syndrome. Journal of Special Education 36, 80–88.
Greenspan, S. (1999). A contextualist perspective on adaptive behavior. In R. L. Schalock & D. L. Braddock (Eds.), Adaptive behavior and its measurements: Implications for the field of mental retardation. Washington, DC: American Association on Mental Retardation.
Sattler, J. M., & Hoge, R. D. (2006). Assessment of children: Behavioral, social, and clinical foundations (5th ed.). San Diego: Jerome M. Sattler.
Schalock, R. L., Luckasson, R. A., & Shogren, K. A. (2007). The renaming of mental retardation: Understanding the change to the term intellectual disability. Intellectual and Developmental Disabilities 45, 116–124.
Wehmeyer, M. L., & Agran, M. (2005). Mental retardation and intellectual disabilities: Teaching students using innovative and research-based strategies. Columbus, OH: Merrill Prentice Hall.
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