Mental Retardation



Historical Timeline


  • Recognize the definition of mental retardation.
  • List the characteristics of mental retardation.
  • List some major accommodations for students with mental retardation.
  • Identify some problems with the definition of mental retardation. 
  • Read history, characteristics, terminology, and notes in this section.
  • Comments on Mental Retardation   Lee Henson, coordinator of Americans with Disabilities in Columbia, Missouri.
  • Comments by Debra MacDonald, mother of a child with disabilities
  • Pregnancy and Alcohol

  • Notes:

    Mental Retardation  - Definition

    Mental retardation refers to substantial limitations in present functioning. It is characterized by significantly sub-average intellectual functioning, existing concurrently with related limitations in two or more of the following applicable adaptive skill areas:

    In practice the diagnosis of mental retardation requires a determination that a child has significantly sub-average intelligence, which is expressed as an IQ score that is more than two standard deviations below the mean.  Depending upon the test, an IQ score below 70 (WISC-R) or 69 (Binet) is considered to be significant.  Performance in all areas of functioning is also expected to be low, and achievement and general development should coincide with the low functioning.  A measure of adaptive behavior is also required in order to prevent culturally "different" children from misdiagnosis, although tests of adaptive behavior have correlated highly with IQ tests, meaning they measure the same traits and are probably interchangeable.  In reporting an IQ, examiners should not disregard the standard error of measurement.  A pupil with a score of 70 could very well have a "true score" above or above 70.  If a mistake is made, the pupil must suffer the consequences by having an inappropriate label attached and opportunities diminished because of lower expectations.

    In many ways, retarded children present opposite characteristics of the gifted but also the same kinds of programming problems.  The majority of children classified as retarded are able to live independently as adults, a small minority require supervised adult living, and only a very small number require care in a private or state facility.  Thus, the majority of children identified as retarded can and will attend public schools and, given proper consideration and programming, will be able to succeed in school and in a vocation.  However, just as in the case of the gifted, the teacher is concerned principally with the vast average group of students and finds it difficult to provide necessary services for the retarded who require individualized attention and assistance.

    Children with mental retardation develop in the same way as people without mental retardation, but more slowly.  By definition, persons with mental retardation have problems with thinking and learning such as attention, perception, or memory. Depending on the extent of the disability there will be different outcomes for academic, social, and vocational adjustment.

    Over 200 causes of mental retardation have been identified, but many others are not known.  The known categories fall into these general classifications:

    Genetic - x-ray exposure, genes inherited from parents, Rh blood factor incompatibility, Down's Syndrome, error in metabolism, or recessive genetic traits.

    Problem in Pregnancy (prenatal)- poor nutrition, measles, tumors, glandular disorders, infections, exposure to toxic agents and drugs, or radiation.

    Birth Problems (perinatal) - premature birth, prolonged birth, reduction of oxygen to the infant's brain.

    Post Birth (postnatal) - disease that affects the brain (chicken pox, measles, meningitis, whooping cough); fever, injuries to the brain, lack of certain chemicals in the blood, or glandular imbalance.

    Environmental Factors - deprived environment and malnutrition.

    Only 3% of the population have mental retardation, and only about 15% of this small group have greater than mild disabilities.
    By comparison to peers, a mentally retarded person passes through developmental milestones more slowly and will be slower to learn and reveal slower development of physical skills. Due to other complications, there may also be concomitant conditions associated with the condition such as physical handicaps, speech impairments, visual impairments, hearing defects, epilepsy, and others.


    The characteristics of mental retardation are somewhat circular, because students are identified and diagnosed on the basis of
    criteria that are later used to describe them.

    Intellectual Skills.   By definition mental retardation means that mental skills are subaverage, so this is the primary

    Adaptive Skills.  Due to the fact that adaptation to one's social and physical environment requires intellectual ability, persons
    with mental retardation are likely to demonstrate significant differences from others.  If they do not, classification as mentally
    retarded is erroneous, despite the measure intelligence quotient.

    Academic Achievement.  Due to subaverage intellectual functioning, persons with mental retardation are likely to be slower
    in reaching levels of academic achievement equal to their peers.  This stands to reason.  However, many students are ultimately
    able to reach some level of literacy, it just takes much longer.

    Motivation.  Motivation is a problem for persons with any disability because it is learned.  Constant comparison to others who
    perform in many areas with apparent ease can be frustrating and diminish motivation, diminish self-esteem, and sometimes create
    "learned helplessness" and belief in failure.

    Speech and Language.  Due to diminished intellectual functioning and associated neurological conditions, many children with
    mental retardation have delayed language and speech problems.

    Physical Characteristics.  As in the case of speech and language problems, mentally retarded persons have slower physical
    development (e.g., toilet training, walking) and are likely to have some forms of associated physical problems.

    Difficulty Attending. Children with mental retardation do not necessarily have more difficulty attending than children of the same mental age, but they are often associated with age peers and the contrasts are more noticeable in terms of developmental delay.

    Impairments in memory, particularly short-term memory.   Research has shown that many persons with retardation have good long-term memory, but they have difficulty remembering in the short term, especially if the facts or complexity of the learning situation are not readily apparent.

    Difficulty with the generalization of skills.  The inability to generalize is related to the inability to think abstractly.

    Limitations in adaptive skill areas. As a consequence of limited intellectual ability, decisions important for adjusting to new circumstances and problems becomes evident in many areas of adaptation to daily activities that require deliberation and decision making.
    Classroom Accommodations

    Providing accommodations for students with mental retardation is similar to learning disabilities, because in many ways the problems of adjusting to the classroom are similar.

    See:  1994 Update on Inclusion in Education of Children with Mental Retardation

    Mental Retardation Criteria

    Intellectual functioning significantly below average.  In general, an IQ of 70 or lower is required.  For persons unable to take a test, clinical judgment is used. .

    Impairments or deficits for age group.  There must be impairments in at least two of the following areas:

    The onset of impairment must be before the age of eighteen.

    Validity and reliability of tests

    Mental retardation is manifested before age 18.  In order to make a valid determination it is necessary to use valid tests and assessment procedures.  Valid assessment must take into account and rule out cultural and linguistic differences.  In addition to subaverage intellectual functioning, which is determined by a test, it is necessary to also determine that there are limitations in adaptive skills that occur within the context of community environments typical of the individual's age peers and is indexed to the person's individualized needs for supports.  Adaptive skill areas are those daily living skills needed to live, work and play in the community. They include communication, self-care, home living, social skills, leisure, health and safety, self-direction, functional academics (reading, writing, basic math), community use and work.

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