Enrollment in public charter schools grew by 250,000 students in the 2015-16 school year, according to a report released Wednesday by the National Alliance for Public Charter Schools. Nationwide, almost 3 million students attend charter schools, nearly three times as many as a decade ago.

Charter schools now serve almost 6 percent of the public school student population. That’s up from just over one percent in the 2001-02 school year. Charter schools didn’t even exist in the United States until 1992, when the first one opened in Minnesota.