Classmates’ academic and executive function (EF) skills are important predictors of individual EF and achievement. The present study investigated the effects of peer EF, using a battery of measures, on individual EF and academic achievement in preschool. Peer effects were assessed for 321 preschool-aged children from 48 classrooms. Using hierarchical linear modeling, peer EF predicted student gains in executive function, vocabulary, and math, but not literacy. Results suggested that classrooms with higher overall EF had students who achieved more skills over the course of the school year in comparison to children in classrooms with lower levels of EF. The effect of fall peer EF on spring student EF was greater for low-income dual language learners (DLLs) than monolinguals. Findings suggest that EF, math, and vocabulary knowledge are socially mediated by peers and can have differential effects on DLLs.