This paper presents an updated WWC (What Works Clearinghouse) Quick Review of the Report "Head Start Impact Study: Final Report". This study examined the effects of offering Head Start to 3- and 4-year-olds. Head Start is a federal program aimed at boosting the school readiness of low-income children by providing preschool education and health and nutrition services. The first follow-up analysis described in this report meets WWC evidence standards with reservations. The second, third, and fourth follow-up analyses described in this report meet WWC evidence standards. [The following study is reviewed in this quick review: Puma, M. et al. (2010). "Head Start impact study: Final report." Washington, DC: Administration for Children and Families, U.S. Department of Health and Human Services. This review is a revision of a quick review released in July 2010. To access this report, see ED510851.]