Mapping the mechanisms of interdisciplinary learning transfer from reading to math achievement: Evidence from a large-scale randomized controlled trial.

Far transfer-the application of learning across distant domains-remains elusive in intervention research, and even when it is found, its mechanisms remain unclear or unexplored. This study analyzes data from the model of reading engagement, a sustained content literacy intervention implemented in Grades 1-3 that demonstrated positive treatment effects on both near-transfer reading and far-transfer math outcomes in a prior study. Here, we extend the original analysis to examine the potential mechanisms of the far transfer effects previously observed on math. Latent mediation analysis shows that approximately 50% of the treatment effect on Grade 4 math is explained by Grade 3 reading, leaving the remainder attributable to other factors. The indirect effects on math are driven by broad standardized reading measures rather than narrower content-specific reading comprehension or background knowledge, suggesting that interventions targeting broad, cross-disciplinary skills may be most effective for supporting far transfer. Results are robust to high levels of unobserved confounding, alternative mediators representing reading engagement and social-emotional learning, and alternative model specifications. We conclude with a discussion of how the appropriate methodological choices for assessing transfer depend on intervention characteristics and substantive research questions. (PsycInfo Database Record (c) 2026 APA, all rights reserved).