Aaron Starke was a 28-year-old assistant principal at a Philadelphia middle school when he heard that Edison Schools Inc. was looking for educators willing to take part in a daring, and potentially disastrous, experiment.

Philadelphia's School Reform Commission had decided to turn over 45 of the city's 265 public schools to such groups as Edison, a for-profit company, in the hope that outside managers with new ideas would succeed where a succession of school boards and superintendents had failed.

High school students demonstrated against the plan. Teachers union leaders predicted that the approach -- alternately known as a "partnership management model" or "diverse provider model" -- would lead to more disappointment.

But Starke, hired by Edison in 2001 to be principal of the Kenderton School in North Philadelphia, has helped raise reading and math achievement. The school has 650 students, almost all from low-income families, in kindergarten through eighth grade.

At Kenderton, where Edison's program of intensive reading instruction and computerized checks of student progress has been implemented, the portion of students scoring proficient or above on a state test has increased 15 percentage points in reading and 25 percentage points in mathematics in the past year.

Although pleased by the gains, Starke pointed out that most of his students still lag. Only 17 percent have reached proficiency in reading and 37 percent in math. "That has to change," he said.

Overall, Edison's 20 schools in Philadelphia averaged a gain of 10 percentage points in the portion of proficient students last year, compared with an average annual gain of less than half a percentage point in the previous seven years before Edison took over, company officials said.

Starke said Edison's close monitoring of students and training of teachers helped him change the school. Before the takeover by outside groups in Philadelphia, he said, "If the kids were quiet and the school hadn't been in the newspaper for anything bad, we would say, 'Hey, we're doing a good job.' "

Other schools managed by what Philadelphia officials call educational management organizations also have showed gains on standardized tests. Twenty-three of them made adequate yearly progress under the federal No Child Left Behind law, up from seven last year.

James E. Nevels, chairman of the Philadelphia School Reform Commission, said this "underscores the promise of the partnership management model, which only two years ago was viewed as controversial and potentially volatile."

But experts say it is far too soon to declare the experiment a success.

Betsey Useem, senior research consultant at the Philadelphia-based Research for Action, a nonprofit organization, said regular Philadelphia public schools also made gains last year, and the private groups might have succeeded in part because the school system "has created one office . . . that clears away the obstacles and bureaucratic barriers" that stymie such efforts.

Gerald W. Bracey, an educational psychologist at George Mason University, cited a recent Philadelphia Inquirer study showing that more than 100 schools in Philadelphia and its suburbs would not have made adequate yearly progress under the federal law if the state had not loosened its rules for reaching that standard.

In the "diverse provider" model, the independent groups take over existing schools with students already in place. This differs from the charter school approach, in which independent groups create schools.

The diverse provider model has the advantage of giving the private groups in Philadelphia -- Edison, Foundations Inc., Victory Schools, Universal Companies, Temple University and the University of Pennsylvania -- a school building. Charter school principals in such cities as the District have struggled to find space.

Several other cities, including New York, Chicago and Los Angeles, are moving toward similar private takeovers. H. Christopher Whittle, founder and chief executive of Edison, said he thought the model might work in the District, where his company has four charter schools, if the superintendent and school board supported it.

Whittle said the Edison schools in Philadelphia have benefited greatly from the backing of the city schools' chief executive, Paul Vallas, and his school board, after weathering the initial opposition from teacher and community groups who opposed having a profit-making company run public schools.

Leaders of other outside groups running Philadelphia schools say they have resources regular schools rarely see. John DiPaolo, executive director for partnership schools at Temple University, said his group's six schools use the university faculty's expertise and have inspired student involvement, including more than 100 students training to be mentors.

Nancy W. Streim, associate dean for educational practice at the University of Pennsylvania's Penn Graduate School of Education, said all teachers at the three public schools it works with "are expected to participate in 120 hours per year of professional development, with many opportunities designed and provided by Penn."

Paul Hill, a University of Washington research professor, has written about the diverse provider model. "Combining real expertise and new freedom is always a good way to get something new and potentially more effective," he said.

But Michael Casserly, executive director of the Council of Great City Schools, a coalition of the nation's large urban school systems, said he thinks a key ingredient in Philadelphia is that both the school district and the outside groups adopted effective curriculums, though they differ in many respects.

"It seems more likely that scores went up across the board because everybody . . . [was] doing a better job teaching the city's children," he said.

Aaron Starke, principal of Kenderton School in North Philadelphia, looks over math problems with Cornelius Middleton, 9.Kenderton seventh-grader Gerera Gilmore, 13, checks out the blackboard.