Out-of-school time programs can enhance academic achievement by helping students learn outside the classroom. The purpose of this practice guide is to provide recommendations for organizing and delivering school-based out-of-school time (OST) programs to improve the academic achievement of student participants. The five recommendations in this guide are intended to help district and school administrators, out-of-school program providers, and educators design out-of-school time programs that will increase learning for students. These recommendations are: (1) Align the OST program academically with the school day; (2) Maximize student participation and attendance; (3) Adapt instruction to individual and small group needs; (4) Provide engaging learning experiences; and (5) Assess program performance and use the results to improve the quality of the program. The guide also describes the research supporting each recommendation, how to carry out each recommendation, and how to address roadblocks that might arise in implementing them. The scope of this practice guide is limited to programs that (1) serve elementary and middle school students; (2) are organized by or conducted in partnership with a school or school district; and (3) aim to improve academic outcomes. Appendices include: (1) Postscript from the Institute of Education Sciences; (2) About the authors; (3) Disclosure of potential conflicts of interest; and (4) Technical information on the studies. (Contains 9 tables, 1 exhibit, and 421 footnotes.) [This report was prepared for the National Center for Education Evaluation and Regional Assistance, Institute of Education Sciences by the What Works Clearinghouse, a project of Mathematica Policy Research, Inc.]