The educational achievement and attainment of young people in the United States has been a long-standing issue of concern. While analyses of long-term trend data from the National Assessment of Educational Progress (NAEP) show that students in the United States have made gains in reading and mathematics over the past few decades, a sizeable proportion of students in this country fail to demonstrate mastery of basic reading and writing skills, lack knowledge about U.S. history or geography, and perform at below-basic levels in mathematics and the sciences. This report synthesizes what is known about the effectiveness of school and program interventions that aim to address deficiencies and inequities in academic achievement and educational attainment by expanding learning opportunities for students both inside and outside of school. In Chapter 1, the authors introduce and frame the topic by providing background on the educational system in the United States and the need for improving the system to better support optimal achievement and attainment outcomes. The introduction also outlines the current policy context, describes the methodology for conducting the literature review, and provides information on the different types of out-of-school time programs. In Chapter 2, they examine the available literature on models in which districts or schools either expand the length of the day that young people must be in school or expand the number of days in the school year. This chapter is divided into two sections: the first looks at the evidence on extended school-day (ESD) program models; the second focuses on findings from extended school-year (ESY) program models. Because this review aims to cover the effects of extended learning time programs serving students in grades K-12, both sections include information on kindergarten programs. Most of the studies of ESD and ESY models focus solely on academic achievement outcomes, so that will be the focus of this review. In Chapter 3, they summarize the effects of social intervention programs that expand learning opportunities outside of the school day by providing at least one academic component as a part of their regular program offerings. In many cases, these programs are designed to complement learning that happens in school. They refer to these programs as expanded learning opportunities or ELO programs. Because ELO programs take place in community and school settings during nonschool hours, these programs are also commonly referred to as out-of-school time (OST) programs. Because random assignment evaluations were available on ELO programs, but not for ESD and ESY program models, Chapter 3 is structured differently than Chapter 2 and focuses on "what works" based on findings from these rigorous evaluations. In addition, the ELO evaluations tended to include information on a wider range of educational outcomes beyond academic achievement; therefore, their review of the research literature on ELO programs in Chapter 3 includes a broader review of educational outcomes, such as information on student engagement and educational attainment. In Chapter 4, they offer a set of conclusions and recommendations based on what they learned from their investigations. (Contains 2 figures, 2 tables, 3 footnotes and 14 endnotes.)