Since its beginning in 1965 as a part of the War on Poverty, Head Start’s goal has been to boost the school readiness of low-income children. Based on a ‘whole child’ model, the program provides comprehensive services that include pre-school education; medical, dental, and mental health care; nutrition services; and efforts to help parents foster their child’s development. Head Start services are designed to be responsive to each child’s and family’s ethnic, cultural, and linguistic heritage. The Congressionally-mandated Head Start Impact Study was conducted across 84 nationally representative grantee/delegate agencies. Approximately 5,000 newly entering 3- and 4-year-old children applying for Head Start were randomly assigned to either a Head Start group that had access to Head Start program services or to a non- Head Start group that could enrol in available community non-Head Start services, selected by their parents. Data collection began in fall 2002 and is scheduled to continue through 2006, following children through the spring of their 1st-grade year. The study quantifies the impact of Head Start separately for 3- and 4-year-old children across child cognitive, social-emotional, and health domains as well as ii on parenting practices. This book is essential reading for those in the education field.