Young children in poor communities are spending more hours in nonparental care because of policy reforms and expansion of early childhood programs. Studies show positive effects of high-quality center-based care on children's cognitive growth. Yet, little is known about the effects of center care typically available in poor communities or the effects of home-based care. Using a sample of children who were between 12 and 42 months when their mothers entered welfare-to-work programs, this paper finds positive cognitive effects for children in center care. Children also display stronger cognitive growth when caregivers are more sensitive and responsive, and stronger social development when providers have education beyond high school. Children in family child care homes show more behavioral problems but no cognitive differences.