Using national data from the Early Childhood Longitudinal Study (ECLS-K), this study examines the association between center-based care duration and intensity and pre-reading, math skills, and social behavior of young children. Children who start center care between ages two and three see greater academic gains, while starting earlier than age two may have negative social effects. Center intensity impacts academic gains for poor and middle-income children, but not wealthier children, and negatively impacts social development for Blacks and whites but not Hispanic children.