The current study was designed to determine whether classroom quality (i.e., the quality of teacher--child interactions) served as a mediator of peer effects with respect to preschool children's gain in language skills over an academic year. Participants were 670 preschool-age children (64.6% boys; "M" = 4 years, 4 months, "SD" = 7 months) enrolled in 83 inclusive early childhood special education (ECSE) classrooms in multiple school districts in a single Midwestern state. Measures included an index of classroom quality, average level of classmates' language skills, and fall and spring language assessments for each child. Results showed that both classroom quality and peer effects contributed to children's language gain over an academic year, showing that both instructional quality and peers are influential to language development. Results did not support a mediating role for classroom quality: that is, classroom quality did not mediate the effects of peers on children's language gain.