Diagnosing Intellectual Disability

Intellectual Disability(ID) is a neuro developmental disorder. ID is characterised by deficits in general cognitive ability such as reasoning, problem solving, planning, abstract thinking, judgment, academic learning and learning from experience. These deficits result in challenges in adaptive behaviour, that is, an individual will have difficulty with the functions and management of personal and social responsibilities. An example of this is cleaning teeth, which will have to be taught with direction over time until the child grasps the process and is able to undertake the activity independently.


A diagnosis is usually made in the developmental period and is characterised by well below average intellectual functioning through a formal diagnosis. A normal range of functioning is considered to be an IQ of 100. Individuals with an IQ of 70 or below are considered to have an intellectual disability. Those with an IQ in the range of 70 – 80 would be considered as having a learning disorder.  A psychologist will use standardised assessment tools in conjunction with talking with the parents of the child to make the diagnosis.

If intellectual disability is assessed it will mean:

IQ(Intelligence Quotient) is assessed as 70 or below

There are deficits in two areas of adaptive behaviour subsets:

  • Communication
  • Daily Living Skills
  • Socialisation
  • Motor Skills

Intellectual disability is further defined in severity of the condition;

Mild Intellectual Disability IQ – 55 to 70

  • Slower than typical in all developmental areas
  • Manages activities in daily life
  • May attain academic skills up to upper primary level or lower secondary in some areas

Moderate Intellectual Disability IQ – 30 to 55

  • Noticeable developmental delays eg speech, motor skills affected
  • May have physical signs of impairment eg Down Syndrome,
  • Will possibly require an alternative method of communication to assist them
  • Will be able to learn basic self care and safety skills

Severe Intellectual Disability IQ – Below 30

  • Considerable delays in all aspects of development
  • May be able to learn some self care tasks or require full attendant care
  • Will have limited or no speech
  • Will not be able to live independently

A child, teenager or adult with an intellectual disability will have varying levels of challenge in managing their lives effectively and independently without support.

Adjusting the environment and providing support and training will increase the individual’s capacity to gain a degree of independence and thus reduce the effect of the disability.

ID can present very differently for each individual. The information gained from the diagnosis will assist parents, the individual, the educational setting and future employer to plan for the present and the future.

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