The current study investigated the extent to which child, family, and classroom factors during Head Start are related to children's literacy and mathematics skills at the beginning of preschool and through first grade. Children and families (n = 945) were participating in the Family and Child Experiences Survey (FACES), a large-scale data collection effort that assessed children's developing skills as well as their family and classroom environments. Longitudinal growth models revealed that Head Start children began their academic careers well below their more advantaged peers in literacy and mathematics, although by the end of first grade, their scores were nearly on par with national averages. Demographic characteristics of children, as well as their early language and social skills, were the strongest predictors of children's initial status and growth in both early academic domains. Results highlight key foundations and specific promotive factors of early school success for the nation's most disadvantaged children. (Contains 5 tables.)