The K-12 and higher education reform programs of the Gates Foundation have been criticized by some education professionals, parents, and researchers because they have driven the conversation on education reform to such an extent that they may marginalize researchers who do not support Gates' predetermined policy preferences. Several Gates-backed policies such as small schools, charter schools, and increasing class sizes have been expensive and disruptive, but some studies indicate they have not improved educational outcomes and may have caused harm. Peer reviewed scientific studies at Stanford find that Charter Schools do not systematically improve student performance