Charter schools now represent 7 percent of national school enrollment. In a growing number of cities, this number is well above 40 percent. This represents one of the most dramatic shifts in the structure of U.S. schooling in the past half century. An entire sector of publicly funded, privately run schools has emerged from scratch that now rivals private schools in its size and scope.
We have learned a great deal from the charter-school experience. Most prior research has focused on how well charter schools serve the students who attend them. These “participant effects” are, on average, small and positive for test scores—more positive in urban areas and in schools using a “No Excuses” approach to instruction and discipline. The results have also generally improved over time, perhaps because charter schools and their partners have had more time to learn from experience.