Not long after Pennsylvania officials announced last spring that Edison Schools Inc. was their choice to run 20 of this city's worst-performing schools, a representative of the firm came to Gillespie Middle School to sell skeptical teachers on the promise of the nation's largest for-profit public school manager. Once the Edison model took hold, the representative assured staff members at the 77-year-old North Philadelphia school, there would be new books for the children, fresh paint on the building and new computers for teachers and pupils. The students, he added, would quietly walk the halls with their arms calmly folded behind...