Osborne said that he had not found another job.
He said he had decided to leave before the official launch in April because most of the programme was in place. David Goldstone, finance director of PFI quango Partnerships UK, will replace Osborne until a permanent successor is found.
The chief executive is likely to have a civil service background and will be in charge of up to 40 people.
The launch had been delayed by legal problems with the procurement process, which have recently been solved.
Yesterday, schools standards minister David Miliband unveiled the first 10 local education authority projects in the programme.