This study sought to determine whether children's adaptive functioning and maladaptive functioning, as measured by the Vineland Adaptive Behavior Scale, are significantly associated with their academic achievement (i.e., Metropolitan Achievement Test [MAT] scores and grade point averages [GPAs]). Differences in the specified functioning and achievement variables resulting from children's grade level, gender, and family structure were also investigated. Subjects were 680 second-, fourth-, and eighth-grade students. Results indicated that several of the adaptive functioning and maladaptive behavior variables were significant predictors of GPAs and MAT scores for White students; only maladaptive behavior was predictive of MAT scores for Black students. Family structure influenced only White students' achievement. Eighth graders had significantly lower GPAs than did second or fourth graders. Implications for future research on children's achievement are discussed.