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.