movement) started by University of Massachusetts professor Ray Budde and American Federation of Teachers leader Al Shanker to explore best practices for education without bureaucracy. However, some critics argue that the charter movement has shifted into an effort to privatize education and attack teachers' unions. For example, education historian Diane Ravitch has estimated, as a "safe guess," that 95% of charters in the United States are non-union and has said that charters follow an unsustainable practice of requiring teachers to work unusually long hours. Better student test scores / Teacher issues According to a study done by Vanderbilt University, teachers in charter schools are 1.32 times more likely to leave teaching than a district-run public school teacher. Another 2004 study done by the Department of Education found that charter schools "are less likely than traditional public schools to employ teachers meeting state certification standards." A national evaluation by Stanford University found that "students attending charter schools have eight additional days of learning in reading and the same days of learning in math per year compared to their peers in traditional public schools". Admissions lottery Because demand often exceeds the supply of available seats in charter schools, lotteries are held to determine which students will be admitted. When admission depends on a random lottery, some hopeful applicants may be disappointed. A film about the admission lottery at the Success Academy Charter Schools (then known as Harlem Success Academy) has been shown as The Lottery. It was inspired by a 2008 lottery. The 2010 documentary Waiting for "Superman" also examines this issue. A lottery, however, ensures those in wealthier districts do not have a better chance of being accepted. Collective bargaining Concern has also been raised about the exemption of charter school teachers from states' collective bargaining laws, especially because "charter school teachers are even more likely than traditional public school teachers to be beset by the burn-out caused by working long hours, in poor facilities." , "an increasing number of teachers at charter schools" were attempting to restore collective bargaining rights. Steven Brill, in his book, Class Warfare: Inside the Fight to Fix America's Schools (2011), changed his position on charter schools and unions. He said that after two years of researching school reform, he understood the complexities. He reversed his view of union leader Randi Weingarten and suggested she run the school system for a city. Racial segregation One study