Supporters believe that the flexibility granted these new public schools allows them to be more innovative and responsive to student needs than traditional public schools are. But do students in charter schools learn more than their counterparts in traditional public schools? In order to answer this question, the authors have analyzed established charter schools in Chicago that are overseen by the Chicago Charter School Foundation. Their results demonstrate that, among students who enter in a typical grade, attending a charter school improves reading and math scores by an amount that is both statistically and substantively significant. They believe that these results can safely be extrapolated to similar schools that serve similar students. In particular, the results are useful for understanding the effects of charter schools run by education-management organizations on student populations that comprise largely low-income and racial/ethnic minorities. Their results should be helpful for many policymakers who are concerned about urban students like those they study. However, they do not claim that the results are helpful for all policymakers. (Contains 5 figures.)