Competence with fractions is important for learning more advanced mathematics. The present study examined the predictive value of sustained attention, verbal and visuospatial working memory, cognitive flexibility, fluid intelligence, multiplication and division abilities for fraction knowledge in fifth grade. Participants were 97 elementary school students from Mar del Plata, Argentina (age range: 10-11). Cognitive and maths-specific abilities explained 38% of the variance in fraction knowledge, with both fluid intelligence and division ability as significant predictors. The results suggest that both general and maths-specific competencies are important for fraction learning.