Executive functions and spatial/relational reasoning relate to individual differences in fraction understanding

• Executive functions and spatial/relational reasoning play different roles in fraction understanding. • Sixth graders relying more inhibitory control and patterning. • Third graders relied more on working memory and whole number knowledge. • Tasks for patterning, number lines, and analogical reasoning may support fraction learning. Studies have shown the importance of executive functions (EFs) and spatial and relational reasoning for fraction understanding; however, few studies have examined them simultaneously. We analyzed two datasets to examine how these domain-general skills contribute to performance in fraction magnitude comparison and number line estimation tasks. In Study 1, third graders ( n = 84) completed working memory and cognitive flexibility tasks, a standardized test of relational reasoning, a whole number line estimation task, and two fraction tasks—fraction comparison and estimation. Cluster analysis showed that participants formed two clusters based on fraction task performance, with one cluster outperforming the other on both tasks; logistic regression showed that working memory and prior knowledge predicted the odds of being classified to the higher-performing cluster. In Study 2, we applied the same analysis to sixth graders ( n = 57), who completed an inhibitory control task, patterning word problems, a standardized math achievement test, and fraction tasks. Results showed the same higher-performing and lower-performing clusters, with prior knowledge (achievement test) as the significant predictor. Results provide initial evidence regarding the joint roles of these skills; however, given the heterogeneity in the measures and designs, which limit direct comparison across our samples, more research is needed to clarify how domain-general and domain-specific skills contribute to fraction understanding.