Edison Schools Inc., one of the nation's largest chains of for-profit schools, is producing student gains roughly comparable with the public schools they replace, Rand Corp. said after a five-year study.

Edison manages 103 schools with about 65,000 students. Average student achievement at its schools didn't exceed that of comparable public schools during their first three years of operation, then matched or exceeded public schools in the fourth and fifth years, according to the Rand report.

The five-year study is one of the most comprehensive reports on the performance of for-profit schools, and may serve as a focal point for the debate in the United States over the role of private industry in public education.

"Some schools have shown extraordinary gains under Edison's management," said Brian Gill, lead author of the report issued by Rand, a nonprofit research company. "But others have not."

Edison hired Santa Monica, Calif.-based Rand in 2000 to conduct the evaluation, then delayed its final report for more than a year. The report today said converted Edison schools experienced "small average declines" in achievement during their first year, and lagged during the first three years, before producing "similar" test scores by the fifth year.

The Rand report said, however, that school-by-school performance varied widely, and schools that most closely implemented Edison's curriculum showed the largest gains in student performance.

"When Edison is allowed to operate unfettered, it has the best results," said Trace Urdan, an education industry analyst with Robert W. Baird & Co. "Unfortunately this sort of perfect laboratory environment is the rare exception in the politics of a school takeover."

President Bush, as part of the federal No Child Left Behind Act, has threatened low-performing public-school districts with takeovers by private entities if they repeatedly fail to show sufficient improvement.

About 60 percent of Edison's schools were conventional public schools later converted to Edison management, usually by local school districts. The remainder are public charter schools, in which a private entity uses public money to operate schools.

The Rand study is "truly comprehensive, but four to five years is longer than most school districts are likely willing to give Edison for a turnaround," Urdan said.

"At the end of the day, the report probably has little effect on its business, with supporters highlighting the strengths and detractors the weaknesses," he said.

Edison has lost contracts to run at least 49 schools in the past three years, said Nancy Van Meter, director of the Center on Privatization at the American Federation of Teachers, the nation's second-largest teachers union.

"Even if they can claim achievement growth at their schools, it hasn't made much difference to most of the districts and charter boards that have canceled contracts with the company over the last three years," Van Meter said.

The 1.3-million-member union issued its own report critical of Edison in February 2003, saying Edison schools performed below average compared with public schools in 14 of the 20 states where the company operates.

The company operates schools in California, Colorado, Delaware, Florida, Georgia, Iowa, Illinois, Indiana, Massachusetts, Maryland, Michigan, Minnesota, Missouri, Nevada, New York, Ohio, Pennsylvania, Wisconsin and the District of Columbia. Most Edison students come from low-income, minority households, Rand said.

Edison also has contracts to work with seven Hawai'i schools, with the schools' existing curricula and staff (see accompanying story).

Gill said Edison failed to fully implement its programs in some cities, and as a result didn't perform better than traditional schools, for reasons including limits on funding and restrictions from current teacher contracts.

Edison's chief academic officer, John Chubb, said those factors generally reflect how willing the school district is to accept the outside company. That points out a potential weakness in the No Child Left Behind law, in which schools may be forced to accept outside leadership, Chubb said.

"There's a potential danger there if a solution is imposed," he said. "The outside provider may be perfectly competent to do the job, but if they're working with schools that are unwilling or reluctant partners, it's going to be difficult to be successful."