Family and child care factors from birth to 54 months, achievement and social outcomes at entry to school, and qualities of first-grade classrooms were used to predict first-grade social functioning for 864 children from the NICHD Study of Early Child Care. Child gender, mothers' partner status, maternal education and depressive symptoms, sensitivity of mothering, and amount of time spent in nonmaternal child care were significant predictors. Home and child care variables predicted social functioning through associations with prior social functioning rather than directly. More teacher-led structured activities in first-grade classrooms predicted mother's reports of more internalizing behavior. Classrooms rated as more emotionally supportive predicted lower levels of mother-reported internalizing behavior and concurrently observed indicators of competence.