Abstract
RESEARCH FINDINGS: The purpose of this exploratory study was to examine the relationship between classroom age composition and preschoolers' vocabulary gains over an academic year and also to examine whether these relations were moderated by classroom quality. In this study (N = 130 children in 16 classrooms representing a subset of all children enrolled in these classrooms), results showed a significant cross-level interaction between classroom age composition and children's age, suggesting positive effects of greater variance in classroom age composition for younger but not older children. The interaction between behavior management (1 dimension of classroom quality) and classroom age composition was also significant, indicating that a wider distribution of classroom age composition was positively related to children's vocabulary gains within classrooms characterized by better behavior management. PRACTICE OR POLICY: Findings underscore the importance of children's social interactions with more knowledgeable conversational partners in promoting their vocabulary development and signify the need to help teachers learn how to manage children's behaviors so as to provide a classroom that is optimal for child learning.