Untangling the Evidence on Preschool Effectiveness Insights for Policymakers Beth Meloy, Madelyn Gardner, and Linda Darling-Hammond JANUARY 2019 Untangling the Evidence on Preschool Effectiveness Insights for Policymakers Beth Meloy, Madelyn Gardner, and Linda Darling-Hammond Acknowledgments The authors thank Sean Tanner for his contributions to the research and our LPI colleagues Barbara Escobar, David Kirp, Michelle Koffa, Patrick Shields, and Marjorie Wechsler for their research contributions, insights, and support. In addition, thanks to Bulletproof Services, Gretchen Wright, and Aaron Reeves for their editing and design contributions to this project, and Erin Chase for overseeing the production and editorial process. Without their generosity of time and spirit, this work would not have been possible. This research was supported by the Heising-Simons Foundation. Core operating support for the Learning Policy Institute is provided by the Sandler Foundation, the Hewlett Foundation, and the Ford Foundation. External Reviewers This report benefited from the insights and expertise of two external reviewers: William T. Gormley, Co-Director of the Center for Research on Children in the United States at Georgetown University, and Martha Zaslow, Director of the Office for Policy and Communications at the Society for Research in Child Development and Senior Scholar at Child Trends. We thank them for the care and attention they gave the report; any shortcomings remain our own. The appropriate citation for this report is: Meloy, B., Gardner, M., & Darling-Hammond, L. (2019). Untangling the evidence on preschool effectiveness: Insights for policymakers. Palo Alto, CA: Learning Policy Institute. This report can be found online at https://learningpolicyinstitute.org/product/ untangling-evidence-preschool-effectiveness. This work is licensed under the Creative Commons Attribution-NonCommercial 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc/4.0/. ii LEARNING POLICY INSTITUTE | UNTANGLING THE EVIDENCE ON PRESCHOOL EFFECTIVENESS Table of Contents Executive Summary.................................................................................................................................. v Introduction ...............................................................................................................................................1 The Structure of This Review .........................................................................................................1 The Preschool Foundation: Results From Early Studies .....................................................................6 The Impact of Preschool: Outcomes of Contemporary Evaluations .................................................9 Evidence of Early Academic Impacts Is Strong ..............................................................................9 Lasting Gains in School Progress Are Common .......................................................................... 10 Academic Advantages Can Persist Into Elementary School ....................................................... 14 Emerging Evidence Points to Benefits for Social and Emotional Learning ................................. 20 Why Do Outcomes Differ Among Programs? .................................................................................... 24 Early Learning Experiences of Comparison Children .................................................................. 24 Measures Related to Long-Term Success ................................................................................... 25 Preschool Program Quality .......................................................................................................... 25 Later School Quality .................................................................................................................... 27 Lessons From Preschool Research ..................................................................................................... 29 Preschool Has Significant Benefits ............................................................................................. 29 Research Should Inform the Design of Effective Programs ........................................................ 30 Appendix A: Literature Selection ......................................................................................................... 32 Appendix B: Unpacking the Methodological Nuances of Preschool Evaluation ........................... 34 Randomized Control Trials .......................................................................................................... 35 Regression Discontinuity ............................................................................................................ 37 Quasi-Experimental Designs ....................................................................................................... 37 Interpreting Effect Sizes .............................................................................................................. 39 Appendix C: Study Descriptions and Findings ................................................................................... 40 Appendix D: Sources for Tables 2 Through 6 .................................................................................... 64 Endnotes ................................................................................................................................................. 70 About the Authors ................................................................................................................................. 80 LEARNING POLICY INSTITUTE | UNTANGLING THE EVIDENCE ON PRESCHOOL EFFECTIVENESS iii List of Tables and Figures Table 1 Programs and Studies of Outcomes Included in This Analysis ........................................3 Table 2 Early Evaluations of Preschool Programs Document Benefits Throughout Adolescence and Adulthood .........................................................................7 Table 3 Preschool Programs Typically Confer Benefits for Children’s Early Academic Skills ..... 11 Table 4 Most Preschool Evaluations Show Positive Effects on School Progress Throughout Childhood and Adolescence ...................................................................... 13 Table 5 Evidence of Academic Effects Throughout School Is Inconsistent ............................... 15 Table 6 Preschool Programs Can Benefit Children’s Social-Emotional and Executive Function Skills ............................................................................................... 23 iv LEARNING POLICY INSTITUTE | UNTANGLING THE EVIDENCE ON PRESCHOOL EFFECTIVENESS Executive Summary Differences in how children develop are substantially linked to differences in children’s learning experiences. As early as 9 months of age, the differential experiences of children growing up in low-income households and children from more affluent homes can lead to a gap in their cognitive development. The developmental gaps continue to grow through elementary and secondary school unless other learning opportunities intervene.1 Inspired by the effectiveness of early preschool programs that have demonstrated significant and sustained benefits for children, many states have invested in such programs to boost children’s early academic skills, narrow achievement gaps, and support children’s long-term academic success. Alongside the growth of early learning programs, the availability of research evaluating the effects of publicly funded preschool has expanded exponentially. Yet making sense of this literature, which includes studies that employ various methodologies to examine diverse programs implemented at different points in time, is a complex endeavor. A large body of research on contemporary preschool programs finds similar benefits for children’s school readiness and later outcomes. However, evaluations of two programs—Tennessee’s Voluntary Pre-K program2 and Head Start3—found mixed results, leaving policymakers and the public confused about how to interpret the findings and what to do to ensure productive investments. This report presents the evidence on the effects of preschool, finding that well-implemented programs support substantial early learning gains and can have lasting impacts throughout school. We explain how the findings from evaluations of the Tennessee Voluntary Pre-K and Head Start programs inform our interpretations of preschool effectiveness and demonstrate how study methodology used to compare children in a program to those outside the program shapes the interpretation of research results. When children who attend a specific preschool program are compared to similar children who did not attend preschool at all—as opposed to those who attended another program—the benefits of preschool are clear. We further note research that finds that the quality of both preschool programs and primary schools can affect the measured outcomes of preschool before and during elementary education. The Evidence Evaluations of contemporary preschool initiatives consistently find that many large-scale programs benefit children’s early academic skills in reading and math. Furthermore, these positive effects on children’s school readiness have been observed in both targeted and universal programs, demonstrating benefits for children across the socioeconomic spectrum. Among the programs included in our review, researchers found clear benefits for participating children’s early literacy skills in