The public debate about the success and expansion of charter schools often seems to gravitate toward a tiny handful of empirical studies, when there is, in fact, a relatively well-developed literature focused on whether these schools generate larger testing gains among their students relative to their counterparts in comparable regular public schools. This brief reviews this body of evidence, with a focus on high-quality state- and district-level analyses that address, directly or indirectly, three questions: (1) Do charter schools produce larger testing gains overall?; (2) What policies and practices seem to be associated with better performance? and (3) Can charter schools expand successfully within the same location? (Contains 8 footnotes and 3 notes.)