Although charter schools engender fierce debate — most recently over ballot measures in Georgia and Washington State — their ranks are growing rapidly, according to a new report. Between 2010-11 and 2011-12, the number of students in charter schools increased close to 13 percent, to just over two million.

The National Alliance for Public Charter Schools, a nonprofit advocacy group, released the report on Wednesday. It showed that in some cities, charter schools — which are publicly financed but privately operated — enroll a significant proportion of public school students.