The Center for Research on Education Outcomes (CREDO) at Stanford University conducted a large-scale analysis of the impact of charter schools on student performance. The center's data covered 65-70% of the nation's charter schools. Although results varied by state, 17% of the charter school students have significantly higher math results than their matched twins in comparable traditional public schools (TPS), while 37% had significantly worse results. The CREDO study strengthens the well-established, broader body of evidence showing average charter performance to be equal to, or perhaps lower than, the performance of traditional schools--a body of evidence that is summarized in this review. The study also presents some state-level analyses concerning policy options; this review points out limitations with those analyses and also explores other policy implications of the report's findings. The relative strength and comprehensiveness of the data set used for this study, as well as the solid analytic approaches of the researchers, makes this report a useful contribution to the charter school research base. Nevertheless, this review points out some weaknesses and areas for improvement, many of which represent commonplace limitations for this type of study that should be shared in the technical report. (Contains 2 tables and 38 notes.)