Arizona enrolls a larger share of its students in charter schools than any other state in the country, but no comprehensive examination exists of the impact of those schools on student achievement. Using student-level data covering all Arizona students from 2006 to 2012, we find that the performance of charter schools in Arizona in improving student achievement varies widely, and more so than that of traditional public schools (TPS). On average, charter schools at every grade level have been modestly less effective than TPS in raising student achievement in some subjects. But charter schools that closed during this period have been lower performing than schools that remained open, a pattern that is not evident in the traditional public sector.