Intellectual disabilities are identified by two key diagnostic criteria. The first criterion is limited mental ability. This is measured by IQ score. Severely limited mental abilities cause many problems. First, it is difficult to learn. Second, it is difficult to make wise decisions and use good judgment. Third, it is not easy solve problems. Fourth, it makes people more vulnerable to victimization.
The second diagnostic criterion is deficient adaptive functioning. Adaptive functioning refers to the skills needed to live independently in a safe and socially responsible manner. There are three essential sets of skills. The first is conceptual skills. These are skills related to language, literacy, mathematics, time, and self-direction. The second set is social skills. These skills help us get along with other people. The third skill set is practical skills. These are the skills needed self-care, employment, health, and safety.
In summary, people with intellectual disabilities may experience a broad range of difficulties. These include problems with communication, self-care, independent living, interpersonal relationships, accessing community resources, self-direction, employment, education, health, and safety.
Possible signs of intellectual disability:
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- Delayed development such as sitting, crawling, standing, walking, or talking;
- Persistence of childlike behavior, possibly demonstrated in speaking style;
- Trouble understanding social rules and customs such as taking turns, or waiting in line;
- Failure to appreciate and avoid dangerous situations such as playing in the street, or touching a hot stove;
- A lack of curiosity or interest in the world around them;
- Difficulty learning new information despite significant effort and repetition;
- Difficulty learning new skills despite significant practice;
- Difficulty solving ordinary, simple problems;
- Trouble remembering things;
- Difficulty meeting educational demands;
- Excessive behavioral problems such as impulsivity and poor frustration tolerance.
When caregivers or teachers notice these signs, they should talk to a qualified healthcare provider. They may recommend a formal assessment and evaluation. It may be difficult to assess very young children for intellectual disability. Therefore, most clinicians are reluctant to diagnose intellectual disability in children less than two years old. The exceptions to this are when a child has a condition that is known to cause intellectual disabilities. A common example would be a child with Down syndrome.
If you have any concerns about your child's social, emotional, physical, or intellectual development, talk to your child's doctor. If your child is school age, also ask to talk with the child's teachers. Sometimes caregivers may notice things that teachers do not, and visa versa. If it appears your child might have an intellectual disability, the school will have your child tested by the school's psychologist (without charge). However, you can be proactive and hire a child psychologist of your own choosing. An assessment will include an evaluation of your child's mental abilities. There are a variety of IQ tests that can be used. The clinician will decide this based on the age of the child. The clinician will also test adaptive functioning. These are practical skills needed to function well within society. The assessment usually includes an observation of the child's behavior and mood at home and school. Typically, caregivers and teachers are interviewed as well. Clinicians will use a variety of different assessment tools and tests. Specific test selection is determined by each clinician.
Intellectual disability versus global developmental delay
It is important to understand the differences between the intellectual disability and another diagnosis called global developmental delay. A diagnosis of intellectual disability should only be made when mental abilities and adaptive functioning (life skills) are significantly below average. The term "developmental delay" indicates that children are slow to reach developmental milestones. This delays may be noticed in speech and language; social skills; motor skills (sitting, walking); or intellectual abilities. However, simply having some developmental delays does not meet the full criteria for intellectual disability. Sometimes a child is too young to be properly assessed. Other times, the child may not be able to complete tests. This may be because certain limitations make testing difficult. For instance, a child with speech or language difficulty may not be able to respond to interview questions. Thus, although children with intellectual disabilities experience developmental delays, not all developmentally delayed individuals have an intellectual disability.
More complete and detailed information can be found in our Intellectual Disabilities Topic Center.