Charter school students are not performing as well as their peers at traditional public schools, according to a landmark report released Monday that also pointed to a need for more accountability at the increasingly popular alternative campuses. The study by Stanford University's Center for Research on Education Outcomes looked at more than 70 percent of the nation's charter school students, providing one of the first national snapshots of their academic performance. Margaret Raymond, the report's author, said the study examined individual student data from schools in 16 states, including California, and found large variations in charter school performance. The study found 17 percent of charter students outperformed traditional schools; 37 percent underperformed traditional schools and 46 percent showed no significant difference. Overall, California's charter school students were roughly on par with their traditionally schooled peers. While the study found charter students on average scored just one percentage point lower in math and less than a percentage point lower in reading than their peers at traditional schools, researchers said it was the first solid evidence of an achievement gap between students learning under the two education models. The findings point to a need for increased scrutiny of the tuition-free public schools, including more aggressive actions to close underperforming campuses, the report said. 'There are people who consider the charter school experiment to be about the functioning of competitive markets,' Raymond said. 'You'd expect underperforming schools would be recognized and students and parents would act accordingly... but whether you're looking at authorizing, closing or parents choosing other schools this part doesn't seem to be working.' The study comes at a time when charter schools are receiving increased attention as President Barack Obama and Secretary of Education Arne Duncan are encouraging the opening of more charter schools. Jed Wallace, president and CEO of the California Charter Schools Association, said he welcomed the findings, which he said echoed his group's cry for more accountability. 'Charter school performance is mixed and improved accountability measures for charter schools would serve the interest of the movement well,' Wallace said. 'A large number of our schools are far exceeding their expectations, becoming some of the best schools in the country, while others are lagging behind. The challenge now is we need to push accountability systems that will result in these schools improving or they will close.' The report pointed out several gains for charter schools revealing that 17 percent of all charters are outperforming their traditional school counterparts. Also, students from low-income families and English language learners fared better in their math and reading test scores at charter schools and students at these schools tended to perform better over time with test scores improving by the second or third year of attendance. The report also found that charters in states that limit the number of charter schools tended to perform worse than charters in states with no caps. Still the Stanford report says education officials should use academic achievement - not just financial and management strength - as a criterion for closing schools. Fundamental to the charter school movement is the reciprocal notion of flexibility in exchange for accountability. Essentially, it means charter schools can have the freedom to educate the way they want to as long as the schools can prove they are doing a sound job. 'Authorizers must be willing and able to fulfill their end of the original charter school bargain: accountability in exchange for flexibility,' the report reads. 'When schools consistently fail, they should be closed.' Jose Cole Gutierrez, executive director of the charter school division at Los Angeles Unified School District, said his office is preparing a new charter policy this week, that calls for more attention to student achievement and test scores when approving or renewing schools. 'Areas we are looking at for sure are academic achievement, finances, governance and fulfilling the terms of charter... any significant concerns in any one of those areas could call for different measures all the way up to school closures,' Cole-Gutierrez said. Overall education experts agree that the report begs for more research into the educational practices inside charter schools, to better figure out what is leading so many to excel and others to fail. 'Charters are designed to educate kids and to provide options for different kinds of educational programs, now we know some are doing really, really well, some are in the middle and some are at the bottom,' said Penny Wohlstetter, director of the Center on Educational Governance at the University of Southern California. 'What we don't know is the difference in educational strategies that the high fliers are using, or the ones that are causing others to not be so successful.' 