What an IQ assessment measures
An IQ test gives a picture of how a person thinks, learns and solves problems compared with others of the same age. The Wechsler tests are the most widely used. Along with a full scale IQ, they give scores for areas such as:
- Verbal comprehension: understanding and using words and ideas
- Visual spatial and perceptual reasoning: making sense of shapes, patterns and visual information
- Fluid reasoning: solving new problems
- Working memory: holding and using information for a short time
- Processing speed: how quickly simple tasks are done accurately
WISC, WAIS and other tests
The psychologist chooses a test that fits the person's age and needs.
- WISC (Wechsler Intelligence Scale for Children, currently the fifth edition): ages 6 to 16
- WAIS (Wechsler Adult Intelligence Scale): ages 16 and over
- WPPSI (Wechsler Preschool and Primary Scale of Intelligence): young children
- Non verbal tests, used when spoken language, hearing or culture would make a standard test unfair
What the scores mean
IQ scores are set so the average is 100. About two thirds of people score between 85 and 115. A score around 70 or below is about two standard deviations below the average, which is the level linked with intellectual disability. Every test has some measurement error, so psychologists report a range, not just one number.
An IQ score on its own does not diagnose intellectual disability. Under the current DSM, diagnosis needs three things: difficulties with intellectual functioning, significant difficulties with adaptive functioning in everyday life, and onset during the developmental period. The DSM sets the severity level (mild, moderate, severe or profound) mainly by adaptive functioning, not by the IQ number.
Why adaptive behaviour matters as much as IQ
Adaptive behaviour means the practical, social and conceptual skills you use every day, such as communicating, looking after yourself, managing money and getting around safely. It is usually measured with a tool such as the Vineland-3 or ABAS, through an interview with the person and someone who knows them well.
For intellectual disability, the NDIA's preferred evidence is, in order: a diagnosis under the current DSM, the Vineland Adaptive Behavior Scale, then the WHODAS 2.0 for people 17 and over or the PEDI-CAT for children 16 and under. So a strong report includes the IQ results, the adaptive behaviour results and a clear diagnosis with its severity.
How it affects NDIS access
Intellectual disability diagnosed and assessed as moderate, severe or profound is on List A. If a treating professional confirms it, the NDIA usually accepts that you meet the disability requirements without more functional evidence. For a mild intellectual disability, you will generally need evidence of how it substantially reduces your functional capacity in everyday life.
Nothing changes about how people access the NDIS until 1 January 2028. From then, access will be based on a standardised assessment of functional capacity, and current participants will be reassessed over 3 years.
Who pays for an IQ assessment
The NDIS does not fund diagnostic assessments, so an IQ assessment to diagnose intellectual disability or to apply for the NDIS is usually paid privately, or done through public child development services, school psychologists or adult disability services where available. Private assessments can be expensive, so ask for a quote that includes the report and feedback session.
Once you are a participant, a cognitive assessment that helps plan or review your supports may be paid from your Capacity Building budget. Psychology has a 2026/27 price limit of $252.99 an hour in most of Australia.