Charter schools — public schools with more freedom to innovate than traditional public schools — have exploded in popularity in the past 25 years. About 6,800 charters now operate in 43 states serving 5 percent of the nation's public school students. Advocates say charter schools provide a superior education, and as proof they cite studies showing that charters have been particularly successful in raising student achievement scores in troubled inner-city districts. Charters do more with less, they say, by eliminating bureaucracy and allowing teachers to try different educational approaches. Critics, however, say that while some charters excel, most do no better than traditional public schools and many do worse. They also accuse charters of cherry-picking the best students and say the charter movement is driven, at least partly, by the desire of for-profit charter operators to make money from public education. Opposition to charter expansion has grown in some states, but President Trump and his new Education secretary, Betsy DeVos, are charter supporters.