In order to make appropriate educational recommendations, psychologists must understand how cognitive test scores influence specific academic outcomes for students of different ability levels. We used data from the WISC-V and WIAT-III (N = 181) to examine which WISC-V Index scores predicted children's specific and broad academic skills and if cognitive-achievement relations varied by general intelligence. Verbal abilities predicted most academic skills for children of all ability levels, whereas processing speed, working memory, visual processing, and fluid reasoning abilities differentially predicted specific academic skills. Processing speed and working memory demonstrated significant interaction effects with full-scale IQ when predicting youth's essay writing. Findings suggest generalized intelligence may influence the predictive validity of certain cognitive tests, and replication studies in larger samples are encouraged.