Directional Associations in Reading and Arithmetic Fluency Development Across Grades 1 to 9: A Random Intercept Cross-Lagged Panel Model

This study explores the directionality of the associations between reading fluency and arithmetic fluency development from Grade 1 through Grade 9 (ages 7 to 16) in a large Finnish sample of 2,518 participants. Participants’ reading and arithmetic fluency skills were assessed at seven time points across Grades 1, 2, 3, 4, 6, 7, and 9. A random intercept cross-lagged panel model (RI-CLPM) was employed to distinguish between between-person and within-person associations. The model revealed a strong positive correlation between reading and arithmetic fluency at the between-person level, suggesting that individuals proficient in one domain typically excel in the other as well. At the within-person level, significant developmental associations emerged predominantly during the early acquisition phase (Grades 1–3). Between Grades 1 and 2, we identified positive bidirectional effects between reading and arithmetic fluency, indicating that variations in one skill predict variations in the other at a subsequent time point. From Grades 2 to 3, a positive unidirectional path from reading to arithmetic was identified, suggesting that variations in reading fluency predict subsequent variations in arithmetic fluency. After Grade 3, no significant cross-lagged paths were identified. These findings highlight the dynamic interplay between reading and arithmetic fluency at different stages of development.