Two critical concerns with the rapid and ongoing expansion of charter schools are that they will segregate students and reduce the per-pupil resources available to conventional public schools. The contradictory prior evidence on such questions is based on potentially misleading cross-sectional comparisons. This study provides new evidence on these issues by conducting panel-based evaluations using school-level data from Arizona and neighboring states. These results suggest that the introduction of charter schools in Arizona has increased pupil-teacher ratios in traditional public schools by 6 percent and reduced the proportion of white non-Hispanic students by 2 percent.