AAIDD, Intellectual Disability and Related Disabilities

Author: Ian C. Langtree - Writer/Editor for Disabled World (DW)
Published: 29 Aug 2009 - Updated: 15 Sep 2026
Publication Type: Journals

Table of Contents:
Synopsis - Definition - Overview - FAQs - Insights, Updates - Related Content

Synopsis

This information provides an overview of the American Association on Intellectual and Developmental Disabilities (AAIDD) and the way intellectual disability, historically termed mental retardation, is defined, classified, and addressed. It notes that the organization publishes two well-regarded journals, the American Journal on Intellectual and Developmental Disabilities and Intellectual and Developmental Disabilities, and outlines the group's core principles around full inclusion, dignity, self-determination, and expanded access to education, health care, and vocational support. The material explains that the condition affects roughly three percent of the population and centers on significantly below-average intellectual functioning alongside deficits in adaptive behavior appearing before age eighteen, while also describing a 1992 system that classifies people by the level of support they need rather than IQ alone. For parents, caregivers, educators, and people living with these disabilities, the value here lies in how clearly it draws together definitions, IQ-based severity ranges, prenatal, perinatal and postnatal causes, testing approaches, and the reality that treatment focuses on building independent living skills rather than a cure.

At a Glance

• 1 - Up to half of all mild cases have no identifiable cause. By contrast, nearly seventy-five percent of severe cases have a cause that can be pinpointed.
• 2 - Down syndrome, Fragile X syndrome and Rett syndrome are among the common causes. Testing can range from chromosomal analysis to an MRI or metabolic screening.
• 3 - The 1992 support-based system rates need as intermittent, limited, extensive or pervasive. This shifts the focus from a single IQ number toward the help a person actually requires.
• 4 - About eighty-five percent of children fall into the mild range, with an IQ of 55 to 69. Many can learn to read and write near a fourth or fifth grade level and live relatively independently with training.

Topic Definition

Intellectual Disability

Intellectual disability, long referred to as mental retardation, is a condition marked by significantly below-average general intellectual functioning that occurs together with limitations in adaptive behavior, with both appearing during the developmental period before a person turns eighteen. In practical terms it has traditionally been tied to an IQ below roughly seventy, which can affect communication and the everyday skills needed for learning, daily living, and work. It affects about three percent of the population and is understood as a spectrum, ranging from mild, where a person may live and work fairly independently with support, to profound, where continuous assistance is needed. Rather than a single disease with one cause or cure, it stems from a wide range of prenatal, perinatal, and postnatal factors, and support today centers on teaching skills that help each individual reach the greatest possible degree of independence and participation in community life.

Overview

The AAIDD is a website and organization that publishes two highly-ranked journals: the American Journal on Intellectual and Developmental Disabilities (AJIDD formerly AJMR), the premier journal in the field, and Intellectual and Developmental Disabilities (IDD), an informative policy and practice journal.

The website itself presents some excellent information regarding intellectual and developmental disabilities and is very much worth any time you take to browse through it. The knowledge you gain through reading items on the site will certainly help.

The AAIDD has a number of principles they follow in order to accomplish their mission. They desire full inclusion and participation for persons with intellectual and developmental disabilities in society, and advocate for equality, individual dignity and additional human rights. The AAIDD works to expand opportunities for choice and self-determination, as well as to influence positive attitudes and public awareness through recognition of the contributions made by people with intellectual disabilities. They promote genuine accommodations to expand the participation of people with these disabilities in every aspect of life while aiding families and caregivers to provide support in the community.

The AAIDD works to increase access to education, quality health, vocational and other human services and supports. The organization advances basic and applied research to prevent or minimize the effects of intellectual disability and enhance the quality of life while cultivating and providing leadership in the field. They seek a diversity of cultures, disciplines, and perspectives in the work they do. The AAIDD also enhances the skills, knowledge and conditions of people in the field, rewarding the work they do. They also encourage students to pursue careers in the field of disabilities while establishing partnerships and strategic alliances with organizations who share their goals and values.

Mental Retardation (MR) affects approximately three-percent of the population. One of the most commonly used definitions of mental retardation is a, 'significant subaverage general intellectual functioning existing concurrently with deficits in adaptive behavior and manifested during the developmental period,' according to the American Association on Mental Deficiency. What this translates to is that the person has an I.Q. below an average of seventy that causes issues with communication, as well as learning the skills that are needed for daily living and working that become apparent before the person reaches the age of eighteen.

While a newer classification system was developed in 1992 which is not based upon the person's I.Q. scores, instead basing the person's classification upon the amount of support and supervision they require, mental retardation is still commonly classified by the child's I.Q. The new system rates the person's support levels as intermittent, limited, extensive or pervasive. The I.Q. rating system is as follows:

Mild: IQ of 55-69

Approximately eighty-five percent of children with mental retardation fall into this range and are further classified as being educable. These children might be able to learn to read and write at the 4th or 5th grade level, live relatively independently and work with special training.

Moderate: IQ of 40-54

Children in this range are described as being trainable. Ten-percent of children with mental retardation fall into this group. These children could have academic potential at the kindergarten or 1st grade level and might have limited ability to read, and commonly need some form of support and supervision related to daily living activities (like with a supportive family or supervised group home) and work (with special training).

Severe: IQ of 25-39

Five-percent of children with mental retardation fall into this group. Children with this level of mental retardation are unlikely to be able to learn to read or write, but might be able to be toilet trained and learn to dress with assistance. They commonly require complete supervision and support for daily living activities.

Profound: IQ of < 24

Less than one-percent of children with mental retardation are in this group.

There are a number of different causes related to why a child has mental retardation, most of them are grouped into prenatal, perinatal, and postnatal causes. These causes might include, yet are not limited to:

• Prenatal causes: chromosomal disorders, including Fragile X Syndrome, gene defects, or exposure to toxins or infections during pregnancy.
• Perinatal causes: prematurity complications, or infection.
• Postnatal causes: infections, lead poisoning or other toxins, metabolic disorders, head trauma.

Up to half of all children who experience mild mental retardation find that there is no identifiable cause related to their disability. Children who experience severe mental retardation are far more likely to have a cause for their disability connected to it, nearly seventy-five percent of these children have a cause of their disability identified. The testing involved in order to identify a cause of a child's mental retardation is dependent upon the particular condition a doctor suspects and varies greatly from child to child.

The testing involved could be limited to chromosomal analysis for Down syndrome or Fragile X syndrome; more extensive testing could be involved such as an MRI scan of the child's brain, or metabolic screening. Testing commonly involves psychological tests in order to evaluate their I.Q. and level of functioning. Common causes of mental retardation include Down syndrome, Fragile X syndrome, and Rett syndrome.

The symptoms a child with mental retardation will experience vary greatly depending on the cause and severity. Generally, children who do not present physical clues, such as a child who experiences Down syndrome, are suspected of having mental retardation when they do not meet age-appropriate developmental milestones. Some children with milder forms of mental retardation are not identified with the disability until they have reached school age.

Where treatment and mental retardation are concerned, it depends greatly on the underlying cause. Generally, there is no cure for mental retardation. Treatment as such is aimed more at teaching a child the skills they will need in order to maximize their independence. Children who have mental retardation may experience additional disabilities as well, referred to as, 'comorbid,' conditions. These conditions include things such as autism, ADHD, depression, anxiety disorders, obsessive-compulsive disorder, epilepsy, cerebral palsy, spina bifida, hydrocephalus, or behavioral issues.

Frequently Asked Questions

Is intellectual disability the same as a learning disability

No, they are different, an intellectual disability involves broad limits in reasoning and adaptive functioning, while a learning disability affects specific skills such as reading or math in a person with typical overall intelligence

Can intellectual disability be diagnosed in adults

Diagnosis requires that signs began before age eighteen, so an adult can be formally identified later in life only if evidence shows the condition was present during the developmental period

What is adaptive behavior

Adaptive behavior refers to the everyday conceptual, social and practical skills a person uses to function independently, such as communication, self care, money handling and getting along with others

Does having an intellectual disability mean a person cannot work

Many people with intellectual disability work successfully, often with special training, job coaching or supported employment, and the level of assistance depends on individual needs and abilities

How is intellectual disability different from developmental delay

Developmental delay describes a young child who is behind expected milestones and may be temporary, while intellectual disability is a lasting condition usually confirmed once a child is older

Can intellectual disability be prevented

Some causes can be reduced through prenatal care, newborn screening, vaccination, avoiding alcohol and toxins during pregnancy and preventing head injury, but many cases cannot be prevented

Why has the term mental retardation been replaced

The term became stigmatizing and is now widely replaced by intellectual disability in clinical, legal and educational settings to use more respectful and accurate language

What support services help people with intellectual disability

Common supports include special education, speech and occupational therapy, vocational training, supported living arrangements, case management and family or caregiver assistance in the community

Insights, Analysis, and Developments

Editorial Note: What makes this piece worth keeping on hand is the way it pairs a national organization's mission with the practical medical framework families encounter after a diagnosis - a combination that is rarely laid out side by side. It is worth remembering that terminology has moved on since this article was first written, and intellectual disability is now the accepted term in clinical and legal settings, yet the underlying structure described here, from adaptive functioning to comorbid conditions such as autism, ADHD, epilepsy, cerebral palsy and hydrocephalus, remains directly relevant to how support is planned today. For caregivers weighing school placement, therapy, or supervised living options, the reminder that many milder cases go unrecognized until school age, and that the right classification hinges on the level of support a person needs rather than a label alone, can shape earlier and more effective decisions.

Author Credentials: Ian is the founder and Editor-in-Chief of Disabled World, a leading resource for news and information on disability issues. With a global perspective shaped by years of travel and lived experience, Ian is a committed proponent of the Social Model of Disability, a transformative framework developed by disabled activists in the 1970s that emphasizes dismantling societal barriers rather than focusing solely on individual impairments. His work reflects a deep commitment to disability rights, accessibility, and social inclusion. To learn more about Ian's background, expertise, and accomplishments, visit his full biography.