The Treasury has taken back £384m originally promised for schools in England - at a time when head teachers are protesting about a cash crisis.
The money had been announced last year to fund a plan to require all schools to become academies. But the Department for Education has revealed that when the compulsory academy plan was ditched, the Treasury took back most of this extra funding.
Heads said this was "outrageous" when schools could not "make ends meet".
But the Department of Education said the return of funds was appropriate if a project did not go ahead.
With warnings from head teachers that lack of funds could force a four-day week, there have been growing questions about the extra cash announced alongside plans to make all schools convert to academies.
Head teachers in West Sussex, who are campaigning against spending cuts, wrote last week to all their local MPs asking what had happened to the extra £500m for schools announced last year by the former Chancellor George Osborne.A letter this week from Bristol head teachers to the education secretary, warning about "extreme" funding problems, also asked why the academy funding cash could not be used. Education ministers had told MPs in April 2016 that there was "over £500m" for the government's academy policy. But the compulsory academy plan was abandoned after a rebellion by backbench Conservative MPs.
And the Department for Education now says most of the extra funding earmarked for schools then disappeared back into the Treasury.
