Intellectual Disability


What is Intellectual Functioning?

Intellectual functioning refers to a general mental capability.  It involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience.  Intellectual functioning is represented by Intelligent Quotient (IQ) scores obtained from standardized tests given by trained professionals.  Intellectual disability is generally thought to be present if an individual has an IQ test score of approximately 70 or below.

What is Adaptive Behavior?

Adaptive behavior is the collection of conceptual, social and practical skills that have been learned by people in order to function in their everyday lives.  Significant limitations in adaptive behavior impact a person’s daily life and affect his or her ability to respond to a particular situation or to the environment.  Standardized testing aims to measure the following skills:

  • Conceptual skills: receptive and expressive language, reading and writing, money concepts, self-direction.
  • Social skills: interpersonal, responsibility, self-esteem, follows rules, obeys laws, is not gullible, avoids victimization.
  • Practical skills: personal activities of daily living such as eating, dressing, mobility and toileting, instrumental activities of daily living such as preparing meals, taking medications, using the telephone, managing money, using transportation and doing housekeeping activities, occupational skills, maintaining a safe environment.


Intellectual Disability is one of several developmental disabilities meaning that there is evidence of the disability during the developmental period of a person’s life.  In California this period of development is defined as occurring before the age of 18.

Characterized by below-average intellectual function, intellectual disabilities impact a person’s day-to-day functioning and last throughout a person’s lifetime. Children with intellectual disabilities may fail to reach developmental milestones in their communications, behavior, play, movement, or learning which will prompt a parent or physician to ask for a comprehensive evaluation.

Children with intellectual disabilities may:

  • sit up, crawl, or walk later than other children
  • learn to speak later, or not at all
  • have trouble with fine motor skills
  • not understand social cues or facial expressions
  • have trouble solving problems

Generally the more severe the intellectual disability the earlier it is noticed. Intellectual disabilities manifest themselves before the age of 18 and generally are lifelong conditions. Usually, an IQ below 70 falls within the range of Intellectual Disability.


It is not precisely known how many people have intellectual and developmental disabilities but most dependable sources tend to agree on a range of 1.5% to 2.5% of the total general population.

Based on the most recent US Census, the US population was reported to be approximately 311 million people which translates to roughly 4.6 million to 7.7 million people with developmental disabilities.  The number of those who specifically have an intellectual disability is lower.


The effects of Intellectual Disabilities vary considerably among people who have them, just as the range of abilities varies considerably among all people.  People with Intellectual Disabilities may need assistance with communications. They may need support with self-care and home living. Additionally, Intellectual Disabilities can effect a person’s social skills and health and safety, their academic work and professional work life.

However with appropriate supports over a sustained period, the life-functioning of the person with Intellectual Disability generally improves. Appropriate supports includes an array of services, supportive individuals, and receptive settings that match an individual’s needs. Every person is different, so each person with Intellectual Disabilities is evaluated and reevaluated so that their needs are being met.

For most people supports are needed over an extended period of time, and for many persons, supports will be lifelong. For some, however, certain supports may be intermittent or short-term. Most people with an Intellectual Disability will improve their functioning with early intervention, appropriate education and supports as an adult allowing them to live a satisfying, meaningful, productive, independent, and integrated life in the community.