Adaptive Functioning & Communication associated with Different Levels of Intellectual and Developmental Disabilities (IDD)

Functioning a, b
Adaptive Functioning a, c
(McCreary 2005)
(Anderson 2002)

  • IQ: 55-70 (± 5)
  • Percentile scores: First to third
  • Age equivalence (AE): 9-12 years
  • Grade: up to Grade 6
  • Unskilled job capability
  • May need income support if jobs are scarce
  • Often develops stable relationships but parenting skills are poor
  • Decision making: likely capable of making familiar medical decisions
  • Uses a variety of sentence types (simple to complex) to communicate opinions, ideas, news, events, aspirations
  • Vocabulary is extensive compared to adults with IDD in the moderate to profound range
  • Uses language to initiate and interact
  • Conversational difficulties may exist
  • Uses the phone and communicates in writing
  • Able to understand and use abstract language but may have difficulty expressing ideas in sequence
  • Can usually follow meaningful, simple, 3-step commands

  • IQ: 40-50 (± 5)
  • Percentile scores: Below the first
  • AE: 6-9 years
  • Grade: up to Grade 2
  • Supported employment
  • Income support
  • Regular residential supervision
  • Help with banking and shopping
  • Childrearing is beyond level of understanding and capacity
  • Decision making: support with medical decisions is required
  • Uses phrases and simple sentences to communicate for various purposes, including expression of preference, emotion, interests and experiences
  • Vocabulary adequate for daily functioning
  • Asks and responds to questions about concrete information
  • Some abstract language use in talking about past events
  • Follows meaningful 2-step commands without support

  • IQ: 25-35 (± 5)
  • Percentile scores: Below the first
  • AE: 3-6 years
  • Grade: up to Grade 1
  • Continuing support and supervision in residential and day programs needed
  • Unable to manage family responsibilities
  • Decision making: not capable of making most medical decisions except if familiar with the issue and provided sufficient support
  • Uses single- and two-word combinations, gestures and/or signs to indicate basic needs and to comment about his/her environment
  • Vocabulary limited
  • Gives and shows objects, points
  • Comprehension still limited to the immediate environment but able to understand some action words
  • Can follow meaningful 1-step commands with or without support (e.g., repetition, gestures)

  • IQ: < 20-25
  • Percentile scores: Below the first
  • AE: 0-3 years
  • Continuing 24-hour support and supervision needed
  • Unable to manage family responsibilities
  • Decision making: can be presumed to be not capable of making medical decisions
  • Nonverbal or uses single words, gestures and/or signs to indicate basic needs
  • A few words possible
  • May appear non-interactive
  • Comprehension limited to people, objects, and events in the immediate environment
  • May follow some routine commands due to understanding the situation rather than the actual words


a. Understanding the intellectual abilities and adaptive functioning of persons with IDD sets the stage for productive clinical encounters. This, in turn, leads to optimal assessments and appropriate treatments. It also promotes better partnership with persons with IDD and enables them to participate in their own health care.

  • Intellectual abilities include reasoning, planning, solving problems, thinking abstractly, comprehending complex ideas, and learning from experience.
  • Different levels of intellectual and adaptive functioning require different types and intensity of supports and service coordination.

b. Levels of intellectual functioning are described in terms of Intelligence Quotient (IQ), Age Equivalence (AE), performance in school and percentiles.

  • This information can be helpful as a general guide but does not always reflect the person with IDD’s individual capabilities.

c. Adaptive functioning or adaptive behavior refers to the skills (conceptual, social, and practical) that a person with IDD has to handle the common demands of everyday life. It is an indication of how independent he or she is, compared to others with IDD of a similar age and level of intellectual functioning.

  • Areas of adaptive functioning that are affected to varying degrees in persons with IDD include self-care abilities, receptive and expressive language, social skills, understanding, learning and remembering new things, self-direction, capacity for independent living, and economic self-sufficiency.

Developed by: Bruce Edwards, Speech-Language Pathologist, Surrey Place Centre, Valerie Temple, Psychologist, Surrey Place Centre and Laurie Dunn, Pharmacist, MUMS.

Original tool: ©2011 Surrey Place Centre.


  1. McCreary BD. Developmental disabilities and dual diagnosis: A guide for Canadian psychiatrists, Kingston, ON: Developmental Consulting Program, Queen’s University, 2005.
  2. Anderson M. In: “Help me speak”: Speech language pathology services provided to individuals with dual diagnosis – reference table: Communication interventions & adults with DD – level of severity and projected outcomes. State of the HART: Habilitative Achievements in Research and Treatment for mental health in developmental disabilities; April 18, 19, 20, 2002; Vancouver, BC: Interprofessional Continuing Education, University of British Columbia, 2002. pp.113-126.