The Philadelphia School District said yesterday that it had narrowed to six the nonprofits eligible to take over some of the city's lowest-performing schools.

The six - they include Mastery Charter Schools and Congreso de Latinos Unidos - were chosen from 28 applicants vying to participate in Superintendent Arlene Ackerman's Renaissance Schools initiative.

Five are Philadelphia groups that operate charters and want to convert district schools into charter schools. The sixth - Johns Hopkins/Diplomas Now, based in Baltimore - has proposed taking over schools but staffing them with district employees.

All the selected organizations have strong academic track records and demonstrated community support, said Benjamin W. Rayer, associate superintendent for charter schools, partnership schools, and new schools.

Next, the six will submit detailed proposals describing their proposed curricula and spelling out how they would achieve academic success at schools with long histories of poor performance.

The groups are:

Aspira Inc. of Pennsylvania, an educational and Latino advocacy organization that operates two charter schools in the city and has been approved by the state to open a cyber charter school.

Congreso de Latinos Unidos, a Latino educational and social services organization that operates a charter school in the city.

The Johns Hopkins program, which runs three turnaround schools in Baltimore and one in Chicago using its Talent Development academic approach, which has been used at several Philadelphia schools.

Mastery Charter Schools, which operates a charter high school and has converted three of the district's troubled schools into charters.

Universal Cos., which has a charter school and a contract to manage three district schools.

Young Scholars Charter School, which operates one charter middle school in North Philadelphia.

District officials announced in January that 14 chronically low-performing schools were candidates for radical restructuring under Ackerman's Renaissance initiative.

The district is slated to announce March 26 how many of the schools will be overhauled in September. The schools will not close, and the students who attend them now will be eligible to remain.

After the district evaluates proposals from the six groups, those that make it to the next round will meet with the advisory councils at the Renaissance schools, which will evaluate the proposed plans.

Ackerman is scheduled to give the School Reform Commission her recommendations for matching schools with operators on May 5. The commission is scheduled to vote on contracts and charter agreements May 19.

Renaissance is part of Ackerman's Imagine 2014 blueprint for academic reform in the district.