Co-developmental trajectories of comparison, ordering, and arithmetic skills for children in grade 2 to grade 4

Digit comparison and order processing performance predict children's later arithmetic skills in the elementary years, presumably because they assess foundational symbolic number knowledge (i.e., cardinal and ordinal associations). However, the influence of earlier arithmetic on later magnitude and order processing has rarely been assessed. Numeracy skills were assessed in two longitudinal cohorts (50% girls) in 2021 and 2022; grades 2-3 (N = 9,552; Mage = 7.4) and grades 3-4 (N = 3,189; Mage = 8.4). A multi-group cross-lagged panel model showed that the longitudinal contributions from earlier arithmetic to later comparison and ordering were stronger (ß = .11-.34) than those in the reverse direction (ß = .03-.09), indicating early math development is both hierarchical and integrated.