The present study evaluated a school district's psychoeducational screening program to determine the best predictors of two difference score variables: (a) WISC-R FSIQ -PIAT reading recognition score and (b) WISC-R FSIQ -PIAT math score. The study also investigated the merit of using scores from a group-administered achievement test (CAT) as predictors. Subjects were 61 first through fifth graders initially referred for testing from 1982-1984. Multiple regression analyses indicated: (a) for reading, the SIQ score and the PPVT-R -CAT reading difference score were significant predictors, together accounting for 27% of the variance, and (b) for math, the PPVT-R score accounted for 28% of the variance, with additional variables producing nonsignificant increments. Results suggest that CAT scores may prove useful predictors when combined with screening IQ tests to form difference scores.