Achievement: Wechsler Individual Achievement Test (WIAT)

What does a WIAT percentile indicate?

It indicates how the child's performance compares with the normative group. For example, the 95th percentile means performance was at or above that of approximately 95% of the normative group, not that 95% of test items were correct.

WIAT ability-achievement discrepancy

The difference between achievement predicted from cognitive ability and the child's actual WIAT achievement score.

When might the WIAT be useful for intervention?

When you need to identify the specific academic skill requiring support and later assess whether the child's performance has improved.

When to choose the WIAT

When you need a detailed assessment of academic attainment, particularly to determine where a child's reading, maths, writing, or oral-language strengths and weaknesses lie.

What does the base rate tell you in an ability-achievement discrepancy?

It tells you how common or unusual a discrepancy of that size is in the normative population. For example, a base rate of <5% means fewer than 5% of similar people show a difference that large, so the discrepancy is relatively unusual and potentially more clinically meaningful.

Why do we need the base rate if the discrepancy is already statistically significant?

Statistical significance tells you whether the difference is reliably large; the base rate tells you whether that difference is unusual in real people. A statistically significant difference may still be fairly common, so both should be considered.

Why use the WIAT with the WISC?

To compare cognitive ability with actual academic achievement and identify an ability-achievement discrepancy.