The association between longitudinal changes in inter-hemispheric IPS functional connectivity and math gains depends on children's age and task requirements.

The role of the approximate number system (ANS) in scaffolding symbolic mathematics remains unresolved. A prior neuroimaging study from our group (Suárez-Pellicioni & Booth, 2018) found no significant longitudinal effects of ANS acuity-indexed by intraparietal sulcus (IPS) activation-on gains in math fluency. However, the absence of age-specific analyses and exclusive focus on fluency, which emphasizes retrieval, may have contributed to these null findings. To address these limitations, the present study examined whether age moderates the relationship between inter-hemispheric IPS functional connectivity during a non-symbolic comparison task and math skill. Specifically, we tested: (1) baseline associations at Time 1 (T1); (2) whether T1 connectivity predicts gains in math skill over time (scaffolding hypothesis); and (3) whether changes in connectivity relate to longitudinal gains. Forty-eight children completed a dot comparison task in the scanner at T1 and again two years later. Standardized measures of subtraction skill and math fluency were collected at both time points. We measured general psychophysiological interaction (gPPI) between IPS seeds and contralateral IPS regions. For subtraction skill, we found no evidence of a concurrent association at T1 or predictive effects of T1 connectivity moderated by age. However, changes in connectivity over time revealed an age-dependent pattern: younger children showed gains linked to increased right-left parietal connectivity, while older children showed gains with decreased connectivity. This suggests a developmental shift from effortful integration to more efficient processing. Effects were specific to subtraction, not fluency.