Invariance of Woodcock-Johnson III scores for students with learning disorders and students without learning disorders.

The purpose of this study was to test the invariance of scores derived from the Woodcock-Johnson III Tests of Cognitive Ability (WJ III COG) and Woodcock-Johnson III Tests of Academic Achievement (WJ III ACH) across a group of students diagnosed with learning disorders (n = 994) and a matched sample of students without known clinical diagnoses (n = 994). This study focused on scores reflecting broad cognitive abilities and areas of academic achievement in which children may demonstrate learning disabilities. Results of this study support the conclusion that the WJ III COG and WJ III ACH measure similar constructs for students with learning disabilities and students without learning disabilities. However, large and pervasive between-groups differences were found with regard to intercepts. Intercepts can be defined as predicted group means for individual tests, in which predicted group means are based on the factor loadings of these tests on the latent variable they are intended to measure. As many intercepts are not equivalent, it is possible that observed scores may not accurately reflect differences in the construct of interest when testing children with learning disabilities. However, tests displaying the largest intercept differences also displayed the largest group differences in observed scores, providing some support for the conclusion that these differences reflect construct-relevant between-group differences. Implications of this research are discussed.