WISC-V scores, explained for parents

The Wechsler Intelligence Scale for Children, fifth edition, is the most widely used children's IQ test in the English-speaking world. It was published by Pearson in 2014 and normed on 2,200 children aged 6 to 16. A psychologist gives it one to one, usually in about an hour (longer if extra subtests are added), with blocks, picture books and spoken questions. Schools use it to look for learning needs, gifted ability, or both at once.

The report looks intimidating because it gives three kinds of number: the Full Scale IQ, the index scores and the subtest scores. They are the same idea at three levels of detail.

Each index is built from two subtests. This is where most of the useful information in a report sits.

Pearson attaches a word to each range. The words changed with this edition: what older reports called "superior" is now "very high", and "borderline" is now "very low". The words describe how the score compares with children the same age, nothing more.

Enter the five index scores to see each as a percentile and in the WISC-V wording, and how uneven the profile is. Nothing is stored or sent. The numbers already filled in are an invented example of a common gifted profile: strong reasoning, average speed.

Many children, gifted children especially, have a profile with peaks and dips. A child might score 132 in Verbal Comprehension and 96 in Processing Speed. The Full Scale IQ then sits in between and tells you little.

A common rule of thumb is that a gap of 23 points or more between the highest and lowest index means the Full Scale IQ should not be the headline. The psychologist will then lean on the index scores and, often, the General Ability Index. An uneven profile is not a diagnosis. It can point to a learning difference worth exploring, and it can just as easily be how your child is built. Ask the psychologist which it is, and why.

Gifted programmes set their own cut-offs, often around 130, the 98th percentile. Two WISC-V numbers matter for them beyond the Full Scale IQ.

The General Ability Index (GAI) uses five reasoning and knowledge subtests and leaves out working memory and processing speed. For a quick-thinking but slow-writing child it is often the fairer number. The US National Association for Gifted Children's 2018 statement on the WISC-V says the Full Scale IQ should not be required for gifted identification and points to the GAI and other indexes as alternatives.

Extended norms. When a child hits the ceiling of several subtests (a scaled score of 19), the standard tables stop at 160. Pearson's Technical Report 6 (2019) published extended norms that let scores go higher for these children. If your child maxed out subtests, ask whether the extended norms were used. Our page on levels of giftedness explains what the bands above 145 mean.

• Is the Full Scale IQ a fair summary for my child, or should we focus on the index scores?
• Was the General Ability Index calculated, and how does it compare with the Cognitive Proficiency Index?
• Are any gaps between index scores unusual for children with this overall level, not just statistically significant?
• What were the confidence intervals, and could a retest in a year look different?
• Did anything on the day (tiredness, nerves, illness, a new place) affect particular subtests?
• What should school do differently because of these results, and what should it not change?

Childhood scores are fairly stable but not fixed, and it is normal for a later test to land several points away. Individual teenagers can move further: in one brain-imaging study of 33 adolescents retested about four years apart, some verbal and non-verbal scores rose or fell by around 20 points (Ramsden and colleagues, 2011). Treat any one test as a snapshot. The why IQ scores differ guide covers retest changes in detail.^[1]