New York, NY —

An effort to keep Mayor Michael Bloomberg in charge of the city schools raised more than $7.5 million.

The lobbying group, Learn New York, was created last year to pressure Albany lawmakers into renewing mayoral control of the city's schools just as the law was about to sunset. The group never revealed who was funding it or precisely how much money it raised, although it insisted Mayor Bloomberg was not a contributor.

One of the funders, Microsoft chairman Bill Gates, personally made a donation, according to the Gates Foundation. Tax filings show Learn New York spent more than $4 million in total-- mostly on a Manhattan office, advertising, staff, and consultants.

More than $3 million of the funds was never spent. A Learn New York spokesman says the remaining money will be returned to the donors now that the group's work is over.