School activists in Philadelphia are challenging the role that two private groups played in developing a plan to overhaul the struggling district.

Parents United for Public Education says the proposal was partly funded by anonymous private donors and developed without public input. The group has filed a complaint with the city ethics board.

The issue has become increasingly relevant as cash-strapped schools nationwide seek nonpublic funding to supplement their budgets.

Supporters say private money can help pay for badly needed innovations. Yet critics say there is not enough transparency about donors' motives.

The issue has also cropped up in New Jersey. Newark officials were recently forced by a judge to publicly disclose details of a $100 million donation from Menlo Park, Calif.-based Facebook Inc. to the school district.