Both federal and state governments regulate the quality and curricula of early childhood education programs in hopes of promoting the school readiness of disadvantaged children. We draw on data from the experimental Preschool Curriculum Evaluation Research Initiative Study to provide an aggregated look at the impacts of four types of preschool curricula (literacy-focused, math-focused, whole-child and locally developed) on classroom processes as well as children's academic and socioemotional outcomes. The math curriculum included in the study boosted both classroom math activities and children's math achievement relative to the two whole-child curricula (HighScope and Creative Curriculum) found in most Head Start and pre-K classrooms. Also relative to HighScope and Creative Curriculum, the literacy curricula increased early literacy achievement despite producing no statistically significant differences in classroom activities or teacher-child interactions. Although Creative Curriculum produced much more positive classroom processes than locally developed curricula, it failed to improve either the academic achievement or behavior of preschool children relative to the local curricula. Implications for Head Start and pre-K curricula choice and the utility of widely used classroom rating scales are discussed. (author abstract)