Using data from the National Early Head Start (EHS) Research and Evaluation Project (N= 1851), the current study examined relations among cumulative family and social risk, assessed during infancy and the preschool years, and children's prekindergarten achievement, self-regulatory skills, and problematic social behavior, testing if these associations were mediated through two sets of family processes--responsive parenting practices and the provision of language stimulation and literacy practices. Structural equation modeling results highlight the significance of the timing of children's experience of risk in predicting school readiness competencies. Risk exposure during infancy was observed to be most detrimental for children's school readiness skills and was partially mediated by risk exposure during the preschool years and family processes, assessed during toddlerhood and the preschool years. Moderation analyses revealed no difference in the strength of relationships among the study variables by EHS assignment or by race/ethnicity. (author abstract)