Book excerpt: Twenty-five years ago, charter schools hadn’t even been dreamed up. Today they are mushrooming across the country. There are 6,500 charter schools operating in 42 states, with more than 600 new ones opening every year. Within a blink there will be 3 million American children attending these freshly invented institutions (and 5 million students in them by the end of this decade). It is philanthropy that has made all of this possible. Without generous donors, charter schools could never have rooted and multiplied in this way. And philanthropists have driven relentless annual improvements—better trained school founders, more prepared teachers, sharper curricula, smarter technology—that have allowed charter schools to churn out impressive results. Studies show that student performance in charter schools is accelerating every year, as high-performing models replace weaker ones. Charter schools as a whole already exceed conventional schools in results. The top charters that are now growing so fast elevate student outcomes more than any other schools in the U.S.—especially among poor and minority children. Charter schooling may be the most important social innovation of our age, and it is just beginning to boom. Philanthropists anxious to improve America have more opportunities to make a difference through charter schools than in almost any other way. This book provides the facts, examples, cautionaries, inspiration, research, and practical experience that philanthropists will need as charter schooling shifts gears from promising experiment to mainstream movement bringing improved opportunity to millions of students.