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Intellectual and Developmental Disabilities

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  • Began in the 19th century, which was earlier than the study of people with most other disabilities.

    • However, professionals efforts were decreasing over time and there wasn't a huge change until the middle of the 20th century

  • The endeavors of social reformers, parents and researchers lead the way to major reforms for the entire field 

    • Their efforts would them go to form the basis of Public Law, now called IDEA

Definitions of Intellectual Disabilities

  • Federal Definition: Significantly subaverage general intellectual functioning, existing concurrently with deficits in adaptive behavior and manifested during the developmental period, that adversely affects a child’s educational performance

  • American Association on Intellectual and Developmental Disabilities (AAIDD) Definition: A disability characterized by significant limitations both in intellectual functioning and in adaptive behavior, as expressed in conceptual, social, and practical adaptive skills.

  • Diagnostic and Statistical Manual Definition: Neurodevelopmental disorders that begin in childhood and are characterized by intellectual difficulties, as well as difficulties in conceptual, social, and practical areas of living.


Causes of Intellectual Disabilities

  • For those with with mild impairments of intellectual disabilities,  the cause of the disability cannot be determined

  • For individuals with more significant intellectual disabilities, the causes are usually considered in terms in when they occurred (during prenatal, perinatal, or postnatal)

  • Some intellectual disabilities are caused by factors before birth--prenatal--resulting in certain conditions, such as a chromosomal abnormality like Down syndrome (aka Trisomy 21), Fragile X Syndrome, Prader-Willi syndrome, and Fetal Alcohol Spectrum disorders

  • When an issue occurs during birth or right after the birth, that causes an intellectual disability, classified as a perinatal cause. This can occur in premature birthed babies or if something happens where the baby doesn't get enough oxygen while being born.

  • A postnatal cause is when an individual has an accident or illness which then develops a intellectual disability, such as lead poisoning, Encephalitis, or a brain injury


  • Cognitive Characteristics: An impact on memory, generalization, metacognition, motivation, language, and academic skills

  • Generalization Characteristics: Difficulties with academic tasks, behavior expectations, and social interactions

  • Social Characteristics: Difficulties picking up on social cues. 

  • Challenges with Metacognition (to think about thinking) and  Motivation

  • May experience development of language delays

  • Students with intellectual disabilities have to work harder and practice longer than other students in order to learn academic skills

  • Deficits in adaptive behaviors like communication, self-care, home living, leisure, health and safety, self-direction, functional academics, and work



  • One common assessment is the Wechsler Intelligence Scale for Children, which assesses intellectual functioning in students being tested for eligibility of special education services

  • An assessment of adaptive behavior is done through surveys from parents and teachers to see how the student is functioning at school, home, and in the community 

  • For individuals with medical factors, there may input needed by medical professionals for the school to know which medications need to be taken, health risks for or limitations needed on physical activities, and chronic conditions

  • Early Childhood: For those born with intellectual disabilities, education starts within a couple months of being born! Early interventionists are usually brought in to help the child with their development. These children will go into preschool at age three where an inclusive class setting will help tremendously!

  • Elementary and Secondary Schooling: The students will, for the most part, be in a general education setting. Depending on the students' level of function determines the extent of which they join their peers in the same activities and how much extra support that is needed. However, some students may spend at least part of the day receiving specialized academic instruction in a special education setting

  • High School: Students at the high school level are more likely to be taught within a special education setting than those at a younger age. However, in some schools, inclusion is emphasized. Depending on the significance of the intellectual disability, some students will leave high school at 18, but some may be require services until age 21. 

  • Inclusive practices, such as the peer buddy system, or the use of paraprofessionals has many benefits for both parties!

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