Nonsymbolic ratio and fraction magnitude processing predict fraction knowledge in early grades.

Understanding the emergence of symbolic math skills during education is important for both theoretical and applied reasons. Here, we specifically focus on the emergence of children's understanding of fractions, a particularly challenging symbolic math skill. Previous studies have demonstrated associations between nonsymbolic ratio perception and formal fraction skills. However, most of those studies measured only concurrent correlations and could not chart development prior to and after formal fraction education. To investigate the emergence of relations between ratio perception and formal math skills, we examined which set of skills prospectively predicted growth in second and fifth graders' fraction skills 1 year later. Results showed longitudinal improvements in fraction knowledge in both groups, with more significant gains occurring earlier in development. A cluster analysis categorized both younger and older participants into two clusters across grades: consistently lower and higher fraction knowledge. Fraction magnitude processing, along with its connections to nonsymbolic ratios, predicted fraction knowledge in both age groups; however, nonsymbolic ratio magnitude processing predicted fraction knowledge only for the younger participants, even when controlling for domain-general factors. Furthermore, nonsymbolic ratio magnitude processing, fraction magnitude processing, and their interrelations differed across clusters of younger participants, whereas nonsymbolic ratio magnitude processing did not differ across clusters of older participants. These findings indicate that nonsymbolic ratio magnitude processing is associated with early acquisition of fraction knowledge, but that understanding magnitudes of symbolic fractions becomes more relevant for fraction knowledge over time. (PsycInfo Database Record (c) 2026 APA, all rights reserved).