This article examines associations between observed quality in preschool center classrooms for approximately 6,250 three- to five-year-olds and their school readiness skills at kindergarten entry. Secondary analyses were conducted using data from four large-scale studies to estimate the effects of preschool center quality and interactions between quality and demographic characteristics and child entry skills and behaviors. Findings were summarized across studies using meta-analytic methods. Results indicate small, but statistically significant associations for preschool center quality main effects on language and mathematics outcomes with little evidence of moderation by demographic characteristics or child entry skills and behaviors. Preschool center quality was not reliably related to socioemotional outcomes. The authors discuss possible explanations for the small effect sizes and lack of differential effects. (Contains 7 tables.)