This study examined the effects of offering Head Start to preschoolers. 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 study analyzed data on about 4,700 preschool-aged children who applied for enrollment for the 2002-03 program year at one of about 380 Head Start centers randomly selected for the study. The study followed the students through first grade. The study compared the outcomes of children who were offered enrollment in Head Start to the outcomes of children who were not offered enrollment. School-readiness outcomes, which are the focus of this quick review, were measured using standardized cognitive assessments of language and literacy, pre-writing, and math skills administered at the end of each year through first grade. The study found that, for 3-year-olds, children offered enrollment in Head Start had higher scores on four of eight measures of language and literacy, the single measure of pre-writing, and one of two measures of math skills at the end of the Head Start year than children not offered enrollment. However, none of these effects were statistically significant when measured at the end of the following year, kindergarten, or first grade. For 4-year-olds, the study authors found that children offered enrollment in Head Start had higher scores on six of eight measures of language and literacy at the end of the Head Start year than children not offered enrollment. However, none of these effects were statistically significant when measured at the end of kindergarten or first grade. There were no significant effects for the measures of pre-writing or math skills. The research described in this report is consistent with WWC evidence standards. A strength is that the groups of students contrasted in the study were formed by random assignment. This quick review cautions that the report contains conflicting information about the sample sizes used in the main analyses of 3-year-olds at the end of their first-grade year and 4-year-olds at the end of their Head Start year, making it difficult to determine the attrition rates for these samples. For this reason, findings from these rounds of data collection should be interpreted with caution. [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.]