Most discussions of charter schools assume that they are monolithic. While the media, researchers, and policymakers are obsessed with comparing charters to traditional public schools, there's been little interest in comparing different types of charter schools to one another--until now. This study--the first of its kind--categorizes the nation's charter schools into a robust typology according to their educational approaches. It also provides demographic information by type--how many are in each category, what their student populations look like, and so forth--and makes a first attempt at comparing their test scores. Appendices include: (1) Charter school typology with distribution by instructional sub-types; and (2) Adjusted, Absolute Means by Type. (Contains 6 figures.) [Foreword written by Chester E. Finn, Jr.]