This study examined whether the Head Start Research-based Developmentally Informed (REDI) program is more effective than the standard Head Start program at improving the language, emergent literacy, and social-emotional skills of preschoolers. Head Start centers in three Pennsylvania counties were randomly assigned either to use the REDI program or to continue using the standard Head Start program. The study included 44 classrooms and 356 4-year-olds across the two research groups. The study assessed language development and emergent literacy skills, as well as emotional understanding, social problem-solving skills, social-emotional behaviors, and learning engagement. Assessments were conducted at the beginning and again at the end of the school year for most outcomes. The study finds that students in the REDI group outperformed control students on one of three measures of language development and two of three measures of emergent literacy skills. Additionally, REDI program students exhibited greater understanding of emotions, better social problem-solving skills, and higher levels of learning engagement than students in regular Head Start classrooms. This What Works Clearinghouse (WWC) review finds that the research described is consistent with WWC evidence standards, and cites the study as a well-implemented randomized controlled trial. A cautionary observation is included that the authors examined the REDI program's effects on more than twenty outcomes. Estimating effects on a large set of outcomes increases the possibility that some results may be found to be statistically significant by chance: the authors do not adjust for this possibility in their analysis. [The following report was the focus of this "Quick Review": Berman, K. L., Dietrich, C. E., Nix, R. L., Geest, S. D., Welsh, J. A., Greenberg, M. T., et AL. (2008). Promoting Academic and Social-emotional School Readiness: The Head Start REDI Program. Child Development, 79(6) (EJ818718).]