Since 1965, Head Start has provided comprehensive services to help prepare the nation's most disadvantaged three- to five-year-old children for school and to strengthen their families. In 1998 Congress instructed the Department of Health and Human Services (DHHS) to conduct an evaluation of Head Start to determine its impact on child development and to identify which children enrolled in Head Start benefit the most. This evaluation, the 2010 Head Start Impact Study (HSIS or Impact Study), adds to a growing body of rigorous research on Head Start and other early care and education (ECE) programs and helps identify the program's strengths and weaknesses. The Impact Study began in the fall of 2002 when researchers began collecting data on nearly 5,000 three- and four-year-olds who were entering Head Start programs. The Impact Study tracked children over time, with findings on children's outcomes at three points--referred to throughout this document as Wave 1, Wave 2, and Wave 3. Wave 1 assessed children's outcomes at the end of their first year of participation in Head Start in 2002 (for groups of three- and four-year-olds). Wave 2 reported on outcomes at the end of kindergarten or first grade year, and is the most recent data available from the Head Start Impact Study. Wave 3, which is currently being analyzed and has not yet been released, will show findings on children's outcomes at the end of third grade. This document provides background information on the Head Start program and discusses key findings from the Impact Study through a series of a questions and answers. It concludes with commentary on the Impact Study from a research perspective, highlighting key policy and practice considerations relating to supporting developmentally appropriate and effective early childhood interventions, specifically noting that: (1) Head Start's whole-child program model is research-based and developmentally appropriate for promoting school readiness and strengthening families; (2) Starting early with high-quality interventions makes a difference; (3) The Impact Study shows how Head Start is contributing to measurable developmental gains for certain subgroups of disadvantaged children. However, rigorous program improvement is needed to improve Head Start's overall effectiveness in supporting the developmental needs of disadvantaged children and their families; (4) In considering program improvements, decision makers would benefit from a better understanding of factors that contribute to successful transitions from early learning settings to elementary school; and (5) Findings from the Impact Study should be considered alongside other research on Head Start and early childhood. (Contains 4 tables, 6 resources and 47 endnotes.