Despite considerable evidence on the links between average classroom quality and children’s learning, the importance of variation in quality is not well understood. We examined whether three measures of variation in observed classroom quality over the school year – overall variation in quality, teacher-specific trends in quality, and instability in quality – were associated with children’s language, literacy, and regulatory outcomes. We also examined whether variation in quality was associated with teachers’ participation in coaching. Overall variation and instability in emotional support and classroom organization over the year were negatively associated with children’s regulatory and literacy outcomes. Participation in coaching was linked to increased variation only in instructional support. We discuss implications for policies focused on improving classroom quality.