The present study examined associations between peers’ EF and gains in individual children’s EF, language, mathematics, and literacy skills across the preschool year, and whether these associations are moderated by classroom quality. Participants included three cohorts of children (n = 556, 52.5% male, Mage = 57.5), their parents, and teachers from a larger evaluation of a state-funded prekindergarten program. Multilevel models indicated that peers’ EF in the fall of preschool was a significant predictor of individual children’s EF (β = 0.14, p = .001), mathematics (β = 0.06, p = .049) and literacy (β = 0.09, p = .027) in the spring of preschool, but was not related to language (β = 0.03, p = .342), while controlling for child and classroom level covariates, fall EF, and relevant pre-academic and language skills. Results from moderation analyses indicated a significant interaction effect between classroom quality and peers’ EF in predicting children’s literacy (β = 0.07, p = .040), suggesting that when children are in low-quality classrooms, having peers with higher EF was more strongly related to gains in literacy skills. No other significant interaction effects were found between classroom quality and peers’ EF in predicting individual children’s EF, language, and mathematics. Implications for future research on peer effects and practice and policy for preschool education are discussed. (author abstract)