The National Head Start Impact Study is a longitudinal study that involves approximately 5,000 three and four year old preschool children across 84 nationally representative grantee/delegate agencies in communities where there are more eligible children and families than can be served by the program. The children participating were randomly assigned to either a treatment group (which had access to Head Start services) or a comparison group (which did not have access to Head Start services, but could receive other community resources). Data collection began in the fall of 2002 and ended in spring 2006, following children through the spring of their first grade year. It includes in-person interviews with parents; in-person child assessments; direct observations of the quality of different early childhood care settings; and teacher ratings of children. Data collection includes the following: Individual child data in the areas related to school readiness, such as physical well-being and motor development, social and emotional development, approaches to learning, language usage and emerging literacy, cognition and general knowledge; Information pertaining to parenting practices, family resources and risk factors, demographic and socio-economic data, and family structure; Information on structure, process, and quality of Head Start, child care, and school settings through first grade; and, Community level data relating to the availability and means of formal and informal family support services. Third Grade Follow-up In 2006, DHHS awarded another contract to Westat and its colleagues (Chesapeake Research Associates, Abt Associates, American Institutes for Research, the University of Virginia Center for the Advanced Study of Teaching and Learning, AMSAQ) to follow the Head Start Impact Study children and their families through spring of their third grade year. This follow-up will examine the following questions: What is the impact of Head Start on children's well-being, and on parental practices that contribute to children's well-being, through their third grade year? For whom and under what circumstances does Head Start have its greatest impact?