The present study investigated the roles of cognitive (working memory, intelligence) and motivational variables (self-perceived ability, intrinsic value) in explaining school achievement. The sample consisted of N=320 German elementary school children in the fourth grade. Working memory and intelligence were assessed in the classroom. Questionnaires including the motivational items were answered at home. Teachers provided midterm and endterm grades for the domains of German and Math. Using structural equation modeling, our main results indicated that across domains, both cognitive and motivational predictors explained substantial amounts of specific variance in school grades. The findings are, however, to some degree domain-specific in that cognitive variables were stronger predictors of Math (COG: β=.59; MOT: β=.41), whereas for German, motivational influences turned out to be better predictors (COG: β=.34; MOT: β=.67). Together, cognitive ability (including both WM and intelligence) and motivation (including self-perceived ability and intrinsic value) explained 75% and 71% of the variance in children's German and Math grades, respectively.