City schools under Philadelphia School District control outperformed those run by outside managers paid millions of dollars to run them, according to a study released today.

The research - which echoes three previous studies - comes at a crucial moment for Philadelphia's privatization experiment, the largest of its kind in the country. The contracts of 18 privately managed schools run by six companies are up June 30, and Superintendent Arlene Ackerman has publicly stated that she will not support schools that don't work.

Conducted by Johns Hopkins University researcher Vaughn Byrnes and published in the May issue of the American Journal of Education, the study found that students at Philadelphia's privatized schools made strides on state exams but that pupils at district-run schools made bigger gains.

Byrnes looked at test scores of sixth, seventh and eighth graders at 88 city schools from 1997 through 2006.

"By 2006, the achievement gap between the privatized group and the rest of the district was greater than it was before the intervention," Byrnes said.

Benjamin Rayer, an associate district superintendent, said last night that the study would help inform the district's decision, and that the administration acknowledged that the private-provider model has produced mixed results.

"If a model is not working, we need to change it, and we intend to do that," Rayer said. "And when a school works, regardless of the form, we're going to do more with that form."

Rayer said that the private-provider contracts did not provide for enough accountability and that would be fixed in any new agreements.

Byrnes' work aligns with three studies that found that district schools outperformed privately managed schools.

Of the 18 school contracts up for renewal, 12 are managed by EdisonLearning, a for-profit company. In a statement, Todd McIntire, regional general manager, noted that the study did not agree with other studies.

A recent study by Harvard University professor Paul Peterson found that students attending schools run by for-profit companies did better in math than those in district-run schools. The study was partially funded by Edison, which runs 20 district schools.

Referring to only the 2008 state test, McIntire said schools run by private companies outperformed district schools.

Privatization has a rocky history in the city. In 2002, 45 failing Philadelphia schools were handed over to outside managers as part of a state takeover of the school district.

Over time, 17 schools were taken back.

Last year, the School Reform Commission warned some operators that unless their performance improved significantly this school year, their contracts would not be renewed.

Today, the outside managers run 28 city schools with roughly 13,400 children. The district spends $6.7 million annually for privately run schools.

In "Imagine 2014," her blueprint for the district's next five years, Ackerman included privately managed schools in the mix. She has said that charter and outside managers with strong track records would be invited to run up to 30 failing district schools.

Jeanne Allen, president of the Center for Education Reform, a proponent of charter schools and school choice, said last night that the study needed to be looked at in broader context. The outside managers took the lowest-performing schools, and they introduced competition, she said.

"Reform kicked traditionally failing schools into gear to do something better, and the addition of charter schools relieved some of the traditional public schools of their worst-off students," Allen said.

But t Helen Gym, a founder of Parents United for Public Education, said the study should send a clear message to the School Reform Commission.

"Philadelphia is probably the last major urban city that's experimenting with this - it's on the tail end, not the cutting edge," Gym said. "We don't think that a lot of these managers have given us the result they promised, despite millions of dollars and years and years of time."

Contact staff writer Kristen Graham at 215-854-5146 or kgraham@phillynews.com.