Charter schools--public schools of choice that are operated autonomously, outside the direct control of local school districts--have become more prevalent over the past two decades. There is no consensus about whether, on average, charter schools are doing better or worse than conventional public schools at promoting the achievement of their students. Nonetheless, one research finding is clear: Effects vary widely among different charter schools. Many educators, policymakers, and funders are interested in ways to identify and replicate successful charter schools and help other public schools adopt effective charter school practices. Charter-school management organizations (CMOs), which establish and operate multiple charter schools, represent one prominent attempt to bring high performance to scale. Many CMOs were created in order to replicate educational approaches that appeared to be effective, particularly among disadvantaged students. Attracting substantial philanthropic support, CMO schools have grown rapidly from encompassing about 6 percent of all charter schools in 2000 to about 17 percent of a much larger number of charter schools by 2009 (Miron 2010). Some of these organizations have received laudatory attention through anecdotal reports of dramatic achievement results. The National Study of CMO Effectiveness aims to fill the gap in systematic evidence about CMOs, providing the first rigorous nationwide examination of CMO achievement effects. The study includes an examination of the relationships between the practices of individual CMOs and their effects on student achievement, with the aim of providing useful guidance to the field. Mathematica Policy Research and the Center on Reinventing Public Education (CRPE) are conducting the study with funding from the Bill & Melinda Gates Foundation and the Walton Family Foundation, and project management assistance from the NewSchools Venture Fund. This report provides key findings from the study on CMO practices, impacts, and the relationships between them. Additional reports will explore promising practices in greater depth and examine longer-term impacts of CMOs on high school graduation and college entry. Appended are: (1) Construction and Analysis of School Practice Measures Used in Chapter III; (2) Validation of The Quasi- Experimental Methods in Experimental Sites; (3) Propensity Score Matching Method; (4) Baseline Equivalence of Student Comparison and Treatment Groups; (5) Method for Dealing With Grade Repeaters; (6) Multiple Comparison Adjustments for Impact Analyses; (7) Impacts by Year and Subject; (8) Impact Estimates for independent Charter Schools; (9) Subgroup Impacts; (10) Methods for Correlating Impacts and Practices; and (11) Detailed Results from Correlation of Impacts and Practices. (Contains 11 tables and 46 figures.) [This report was written with assistance from Michael Barna, Emily Caffery, Hanley Chiang, John Deke, Melissa Dugger, Emma Ernst, Alena Davidoff-Gore, Eric Grau, Thomas Decker, Mason DeCamillis, Philip Gleason, Amanda Hakanson, Jane Nelson, Antoniya Owens, Julie Redline, Davin Reed, Chris Rodger, Margaret Sullivan, Christina Tuttle, Justin Vigeant, Tiffany Waits and Clare Wolfendale. For related report, "The National Study of Charter Management Organization (CMO) Effectiveness. Report on Interim Findings," see ED516865.]