The accumulated data from studies of the WIAT-II, including content, construct, and criterion related evidence of validity, indicate that the subtests and composites adequately measure the achievement constructs that they were designed to measure.
Correlations of the WIAT-II scores with other achievement test scores are moderate to high and consistent across a variety of individually and group-administered tests. In addition, the mean standard scores are consistent over a variety of samples administered the WIAT-II and other individually administered achievement tests.
This pattern indicates that the level of performance of the WIAT-II standardisation sample aligns well with performance on comparable tests and is in the expected range. Correlations from .25 to .82 are typical of the relation between the WIAT-II scores and the scores on the Wechsler scales.
Data on clinical studies show expected patterns of mean standard scores, although the samples were relatively small and not intended as randomly stratified normative groups. Data from the special group studies illustrate that the WIAT-II subtests are effective in identifying large percentages of individuals with these disabilities.