The 2013 Washington State Legislature directed the Washington State Institute for Public Policy (WSIPP) to review "the research evidence on components of successful early education program strategies" for low-income children. In this report, we present findings from our analysis of early childhood education (ECE) research. We conducted this analysis by reviewing all credible evaluation studies from the United States and elsewhere. We systematically analyzed the studies to estimate whether various approaches to ECE have a cause-and-effect relationship with outcomes for low-income students. We then calculated whether the long-term monetary benefits of ECE investments outweigh the costs. Research on ECE programs serving low-income children can provide insight on the effectiveness of Washington's own program, the Early Childhood Education and Assistance Program (ECEAP). The 2013 Legislature also directed WSIPP to "conduct a comprehensive retrospective outcome evaluation and return on investment analysis" of ECEAP. That evaluation will be completed by December 2014. The full legislative direction to WSIPP is in Exhibit 1 (next page). In this report, we first describe WSIPP's approach to systematic research reviews and benefit-cost analysis. We then highlight our findings on the average effectiveness of ECE for low-income children. (author abstract)