The current study was designed to investigate how the quality of stimulation and support available to children in the home interacts with participation in Early Head Start to determine children’s development. Data were obtained as part of the national evaluation of Early Head Start (EHSRE), a randomized trial involving 3,001 children and families from 17 program sites. Hierarchical linear regression analyses were used to examine the interaction of EHS with (a) early maternal emotional warmth and (b) provision of a stimulating home environment on children’s development at ages 3 and 5. Findings showed EHS sometimes differentially benefited children who came from households where the levels of warmth and stimulation were lowest. However, there was evidence of other forms of moderation as well.