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Mental Retardation: Update 2002


The ERIC Clearinghouse on Disabilities and Gifted Education (ERIC EC)
E-mail: webmaster@hoagiesgifted.org
Internet: http://eric.hoagiesgifted.org
ERIC EC Digest #E637
Author: Jack Hourcade
November 2002
Overview and Definition

Mental retardation is a complex phenomenon, and fundamental beliefs about it regularly change over time. Mainstream professional thought today conceptualizes it as a statement about an individual's present level of functioning, with two primary features:

  • Limitations in intelligence
  • Limitations in adaptive behavior.

The American Association on Mental Retardation (AAMR), arguably the leading professional organization in the field of mental retardation, offered the following definition of mental retardation in 2002 in its 10th edition of the AAMR reference manual on definition and terminology (Luckasson, Borthwick-Duffy, Buntinx, Coulter, Craig, Reeve, et al.):

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.

This definition has been widely adopted. It forms the basis for the definition included in IDEA, the Individuals with Disabilities Education Act of 1990.

Intelligence may be thought of as one's overall mental ability, one's capacity to problem-solve and learn. Assessment of intellectual functioning has remained controversial for over a century, ever since Alfred Binet developed the first version of what has come to be known as IQ tests. These tests typically include a range of items that assess one's general knowledge, vocabulary, problem-solving skills, and reasoning ability.

Most IQ tests are structured so that a score of 100 is considered average. The determination, then, of what is considered to be a "significant limitation in intellectual functioning" remains somewhat arbitrary, the equivalent of a line in the sand. Prior to 1973, the recommended IQ cut-off score for mental retardation was 85. In 1973, that was revised downwards to approximately 70, where it remains today. This is roughly the lowest scoring 2% of the population.

The low IQ score alone is insufficient for a diagnosis of mental retardation. It must co-exist with limitations in adaptive behavior. Adaptive behavior refers to those social and practical skills that people use to effectively function in their everyday lives. These include skills in such areas as communication, social interactions, taking care of oneself, managing money, and using transportation, among others. Various tests of adaptive behavior assess skills by either observing the individual in situations where these skills are required, or by interviewing those who know the individual well.

An accurate diagnosis of mental retardation thus requires three components:

  • An IQ score of approximately 70 or below
  • A determination of deficits in adaptive behavior
  • Origins of the disability prior to age 18.

Levels of Mental Retardation

Traditionally mental retardation has been divided into four levels of severity, based largely on IQ scores:

  • Mild mental retardation, IQ scores from 70 to 55/50
  • Moderate mental retardation, IQ scores from 55/50 to 40/35
  • Severe mental retardation, IQ scores from 40/35 to 25/20
  • Profound mental retardation, IQ scores below 25/20

Typically these levels are used more in clinical settings. In school settings, terms such as "severe disabilities" or "profound disabilities" are more commonly found.

In 1992 the AAMR proposed a reconceptualization of levels of mental retardation based not on IQ scores, but instead on the level of support the individual requires in order to function successfully in society. This system included the following four levels:

  • Intermittent support (episodic need)
  • Limited support (needed for specific periods of time)
  • Extensive support (needed regularly for an extended period of time)
  • Pervasive support (life-long, intense need).

To date, this "levels of support" system has not been accepted as widely as the traditional system based on IQ scores (Conyers, Martin, Martin, & Yu, 2002).

Prevalence Rates

Approximately 1% of school-aged children presently are receiving special education services under the category "mental retardation" (U.S. Department of Education, 2000). This figure has declined significantly over the past 25 years, perhaps because diagnosticians are more skilled in differentiating these individuals from those who have other disabilities such as autism and attention deficit hyperactivity disorder (ADHD). In addition, there may be some reluctance to make a diagnosis of "mental retardation" due to increasing stigma associated with that term.


Individuals with mild mental retardation typically do not have any specific physical or medical cause for the limitations in intellectual functioning and adaptive behavior. In these cases the cause is more likely to be heredity (parents who themselves were below average in intelligence), early environment (lack of linguistically and intellectually stimulating experiences), or some combination thereof. One significant exception to this is fetal alcohol syndrome, wherein women who drink alcohol during their pregnancies are at high risk of giving birth to babies with mild to severe intellectual impairment, as well as other problems such as ADHD. As a general rule, the more severe the mental retardation is, the more likely it is to have an identifiable medical or physical cause. These include chromosomal abnormalities such as Down Syndrome and Fragile X, metabolic disorders, and other conditions that result in insult and injury to the brain and central nervous system.


In general, people with mental retardation are less efficient at learning than are other people. This impairment in learning efficiency is roughly consistent with overall IQ level. Specific cognitive deficits often exist in such areas as memory, attention, or language.

In addition, individuals with severe mental retardation are more likely to have brain damage, which in turn is associated with such physical disabilities as cerebral palsy and seizure disorders (epilepsy) and their associated physical characteristics.

Educational and Adult Programs

IDEA entitles every child with mental retardation from age 3 through 21 to a free appropriate public education through an individualized education program (IEP). School is more than the acquisition of academic skills. It provides all students, including those with mental retardation, with the opportunities for social development. Classroom programs such as "Study Buddies" or peer tutors can help students with mental retardation by pairing them with selected classmates in cooperative learning arrangements to facilitate the acquisition of both academic and social skills.

Students diagnosed with mental retardation and receiving special education services should be provided with access to the general education curriculum, so that they can interact with and learn from and alongside typical classmates. This can be achieved through accommodations and modifications to the classroom's curriculum and instruction. Special attention should be given to the development of functional academic skills for these students. Functional academics refer to reading and mathematics skills that are used frequently in everyday life (e.g., reading signs or instructions, counting change, or taking measurements).

As these individuals move to secondary education settings, the curriculum should take on a stronger career preparation and life skills emphasis. With appropriate preparations, even individuals with severe intellectual disabilities can acquire vocational skills, and as adults can move into productive roles in the work place. It is increasingly expected that adults with mental retardation will work in inclusive work settings alongside typical workers with supports provided there as needed, and that these individuals will live in residential programs that represent the sorts of homes that most people live in.

The Future of Mental Retardation

The term "mental retardation" has been the term of choice for individuals with significant limitations in intellectual functioning and adaptive behavior for many decades now. However, as was the case for its predecessor term "mental deficiency" (or even earlier, such terminology as "idiot," "imbecile," and "moron"), over the past few years the term "mental retardation" has lost much professional acceptance.

For example, in 1953 the National Association for Retarded Children was formed. Through the years and several name changes the term "retarded" was retained in the name of that organization until 1992. At that time the organization name was changed to simply "The Arc," eliminating any reference to mental retardation.

In 2002 the Council for Exceptional Children's Division on Mental Retardation and Developmental Disabilities voted overwhelmingly to change its name to The Division on Developmental Disabilities (Stodden, 2002). In deciding to remove the term "mental retardation" from their name, they concluded that the term:

  • Was offensive
  • Excluded many individuals with cognitive and intellectual disabilities, including those with autism
  • Had been replaced by many states with such terms as intellectual impairment or cognitive disability.

Similarly, the American Association on Mental Retardation is presently engaged in extensive discussions concerning a potential organizational name change, perhaps to "The American Association on Intellectual Disabilities." While a final decision had not been reached by October 2002, it appears likely that the change will occur.

Names and terminologies change over time. However, this must not be allowed to distract professionals and families from what should be the paramount concern. Individuals with mental retardation must be provided the types and levels of supports in school, work, and residential environments that will enable them to enjoy the same quality of life that is available to others in society.


American Association on Mental Retardation (AAMR)

The Arc

Beirne-Smith, M., Patton, N. R., & Ittenbach, R. (2001). Mental retardation (6th ed.). Upper Saddle River, NJ: Prentice Hall.

Blatt, B., & Kaplan, F. (1966). Christmas in purgatory. Boston: Allyn and Bacon.

Conyers, C., Martin, T. L., Martin, G. L., & Yu, D. (2002). The 1983 AAMR Manual, the 1992 AAMR Manual, or the Developmental Disabilities Act: Which do researchers use? Education and Training in Mental Retardation and Developmental Disabilities, 37, 310-316.

Council for Exceptional Children, Division on Developmental Disabilities

Drew, C. J., & Hardman, M. L. (2000). Mental retardation: A life cycle approach (7th ed.). Upper Saddle River, NJ: Prentice Hall.

Exceptional Parent

Luckasson, R., Borthwick-Duffy, S., Buntinx, W. H. E., Coulter, D. L., Craig, E. M., Reeve, A. et al. (2002). Mental retardation: Definition, classification, and systems of supports (10th ed.). Washington, DC: AAMR.

National Down Syndrome Congress

Stodden, R. A. (2002). Division completes name change. MRDD Express, 12(3), 8.


Turnbull, A., & Turnbull, H. (2001). Families, professionals, and exceptionality: Collaborating for empowerment (4th ed.). Upper Saddle River, NJ: Prentice Hall.

U.S. Department of Education. (2000). Twenty-second annual report to Congress on the implementation of the Individuals with Disabilities Education Act. Washington, DC: U.S. Government Printing Office.

ERIC Digests are in the public domain and may be freely reproduced and disseminated, but please acknowledge your source. This publication was prepared with funding from the Office of Educational Research and Improvement, U.S. Department of Education, under contract no. ED-99-CO-0026. The opinions expressed in this report do not necessarily reflect the positions or policies of OERI or the Department of Education.

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