WASHINGTON -- Students in charter schools, often seen as an alternative to failing neighborhood schools, are scoring significantly below public school pupils in basic reading and math skills, a new study shows.

Charter school students were anywhere from a half year to a full year behind their public school peers, researchers at the Brookings Institution concluded after reviewing 1999-2000 reading and math achievement test scores of 376 charter schools in 10 states.

The study, the first independent snapshot of charter school performance across the nation, found that 59 percent of students at traditional public schools scored better than charter school students during the period studied.

The findings don't necessarily reflect poorly on charter schools, which often attract students who are looking for a way to improve their skills, the authors caution.

In a few states, such as Texas, these schools actively seek out such pupils, said Tom Loveless, a senior fellow at the Brown Center on Education Policy at Brookings, a liberal-oriented think tank here. "They're out looking for kids who are low-achieving," he said.

Jeanne Allen, president of the Center for Education Reform, a Washington organization that advocates for charter schools, said more information is needed on how much students learn after they've spent a few years in a charter school.

Charter schools are public schools that have signed an agreement with their states to improve students' education.

Generally overseen by an independent board and given greater freedom over budgets, hiring and purchasing, charter schools can be opened by nonprofit groups, churches, universities, community centers, parents, groups of teachers and school districts.

About 2,400 charter schools served more than half a million children during the 2001-2002 school year. More than half of those -- about 1,300 -- opened in the past three years alone. Allen said nearly 400 are opening this fall.

The Brookings study looked at schools in Arizona, California, Colorado, Florida, Massachusetts, Michigan, Minnesota, Pennsylvania, Texas and Wisconsin.