Competence with fractions predicts gains in mathematics achievement

► The relations between fractions knowledge and math achievement was assessed across 6th and 7th grades. ► Fractions knowledge in 6th grade predicts gains in math achievement from 6th to 7th grade. ► Math achievement in 6th grade does not predict gains in fractions knowledge from 6th to 7th grade. ► Fractions procedural skills predict mathematics achievement controlling for other factors. ► Fractions procedural skills do not predict reading fluency, once other factors are controlled. Competence with fractions predicts later mathematics achievement, but the codevelopmental pattern between fractions knowledge and mathematics achievement is not well understood. We assessed this codevelopment through examination of the cross-lagged relation between a measure of conceptual knowledge of fractions and mathematics achievement in sixth and seventh grades (N=212). The cross-lagged effects indicated that performance on the sixth grade fractions concepts measure predicted 1-year gains in mathematics achievement (ß=.14, p.50). In a follow-up assessment, we demonstrated that measures of fluency with computational fractions significantly predicted seventh grade mathematics achievement above and beyond the influence of fluency in computational whole number arithmetic, performance on number fluency and number line tasks, central executive span, and intelligence. Results provide empirical support for the hypothesis that competence with fractions underlies, in part, subsequent gains in mathematics achievement.