Charter schools are elementary or secondary schools that receive public money but have been freed from some of the rules, regulations, and statutes that apply to other public schools in exchange for some type of accountability for producing certain results, which are set forth in each school's charter. Charter schools are opened and attended by choice. While charter schools provide an alternative to other public schools, they are part of the public education system and are not allowed to charge tuition. Where enrollment in a charter school is over subscribed, admission is frequently allocated by lottery-based admissions. In a 2008 survey of charter schools, 59% of the schools reported that they had a waiting list, averaging 198 students. Some charter schools provide a curriculum that specializes in a certain field — e.g., arts and mathematics.