The school budget shortfall has resulted in more than 200 teachers being made redundant, a survey suggests.
Teacher redundancies are 'not acceptable', the NASUWT says
The NASUWT union found employers in England had dismissed 696 staff - 237 of them because of financial problems.
More than 1,500 teachers had received redundancy warning notices.
But fewer than half of these had resulted in actual layoffs by the May 31 deadline for this academic year.
A BBC survey last week found the number of notices had been 1,400.
'No redundancies are acceptable'
NASUWT general secretary Eamonn O'Kane said: "Our comprehensive survey is important because it gives the actual dismissal figure, as opposed to the possible redundancies contained in notices.
"The figure of 1,507 reflects those of the recent BBC survey, but the actual dismissals of 696 fall well below those possible redundancies.
"Of course, no redundancies are acceptable, but our negotiating secretaries reported that in most local education authorities the redundancies will be from volunteers or will result in redeployment."
The survey was conducted in 59 of England's 150 LEAs.
It found employers had issued 589 notices before May 31, which, when applied to the country as a whole, would mean 1,507.
Of those notices, 258 resulted in dismissal. Across England as a whole, this would mean 696.
Half were caused by falling pupil numbers, 34% by funding shortfalls and 16% by other factors, including school reorganisation.
Mr O'Kane said: "Another important factor to note is that the majority of the redundancies have been caused by falling rolls or school reorganisations, rather than specific budget shortfalls.
"The problems caused by falling rolls and school reorganisation occur annually and, of course, can be more pronounced in one part of the country than another."
The Department for Education and Skills has not released figures for redundancy notices or dismissals.
The shadow education secretary, Damian Green, said: "It is very clear from this survey that hundreds of teachers are being sacked because of the government's funding crisis and that (the Education Secretary) Charles Clarke was simply wrong when he told the House of Commons that redundancies would be at the same level as previous years.
"He could solve this crisis with a small part of his own department's underspent budget.
"I am at a loss to know why he persistently refuses to do this."
Despite a £2.7bn increase in education funding this year, schools are still facing budget deficits of up to £500,000.
Head teachers are blaming the problem on insufficient funding for higher teachers' wages, National Insurance and pension contributions.
Mr Clarke has indicated he will change the way schools are funded next year and provide minimum cash increases for each.
In a speech to the Local Government Association (LGA) annual education conference, in Manchester, Mr Clarke said central and local government had to share responsibility.
He wanted to empower head teachers to "lead the charge" for higher standards for every pupil.
It was the job of the LEAs to "facilitate" that.
He proposed a 10-point deal between the government and LEAs which set out their responsibilities.
Speaking at the same LGA conference, Damian Green said the worst outcome from this year's funding crisis would be a new system devised in a hurry.
I think there should be a radical cut in the power of government to interfere in the day-to-day running of our schools
Shadow education secretary, Damian Green
He called for "a road map" by which schools could become autonomous.
"I think there should be a radical cut in the power of government to interfere in the day-to-day running of our schools," he said.
"I want this because the decisions that will improve the performance of schools year after year have to be made by heads, teachers, governors and parents.
"If a school wants to be autonomous, and they have met some transparent criteria about standards in performance, discipline and governance, it will be their choice as a school whether they accept autonomous status."
They would then have control over how they spent their money, which would come to them in a direct lump sum.