Charter schools offer something that public school systems, parents, and teachers need: a way to experiment with alternative ways of teaching, motivating students, organizing schools, using technology, and employing teachers. While people came down on both sides of support for or against charter schools, everyone was surprised by how difficult it was to assess charter school performance. The first part of this book focuses on how to improve estimates of charter schools’ performance, especially their benefits to students who attend them; the second part suggests how policymakers can learn more about charter schools and make better use of evidence. The editors and authors suggest ways states and localities can improve the quality of data on which charter school studies are based and trace some of the ways charter school research influences policy.