A further funding crisis could hit schools this autumn when they will get only a third of the extra money they were expecting for sixth forms.
The 1,800 schools with sixth forms will be up to pound;60 million short, despite government guarantees to protect budgets when they announced funding reforms in 2001.
Instead of the 10.5 per cent rise expected, sixth forms will get around 3.5 per cent. This will add to the shortfalls in budgets many schools already face.
Headteachers say it will lead to a dramatic rise in post-16 class sizes, cuts in the range of courses on offer and pressures on schools to put students on inappropriate courses simply to boost funding for them.
School sixth-forms are funded by the Learning and Skills Council, which took control of budgets from local education authorities under a wider package of post-16 reforms introduced last year. With these came a change in approach to funding. Instead of schools being paid up to pound;4,000 for each A-level student, they get pound;730 for each A-level the student does.
Ministers responded to heads' protests over cuts of up to pound;1,000 a year per student by giving a guarantee that sixth-form budgets would be protected "in real terms".
The amount paid by the LSC rises to pound;755 per student per course this September. There will also be extra cash for other contingencies. But the total falls well short of the guarantee, said John Dunford, general secretary of the Secondary Heads Association.
Sue Glanville, head of Invicta grammar school in Kent and a member of the local LSC, said: "We already have to find a pound;200,000 cut for next year and this will only make things worse. The total pot is too small and the complex mechanism to get the cash into schools is not working."
The problems were compounded by escalating costs, such as A-level exam fees, she said. "My LSC officials tell me the money they have will not cover our costs."
A national LSC spokesman said: "We have added pound;30m to what the department has given us and will try to make sure the money is allocated as efficiently as possible."
A Department for Education and Skills spokesman described heads' claims as "nonsense" and said budgets had gone up 5.3 per cent plus pound;40m for staff pensions. "There is no evidence that any school where pupil numbers have been maintained has lost out," he said.
Leader, 26; FE Focus, 43