The government should "come clean" over its "incompetent" handling of school finances, which has left many with six-figure funding shortfalls, the leader of Britain's biggest teachers' union has said.
Doug McAvoy, general secretary of the National Union of Teachers (NUT) said resources were being cut in an effort to balance the books, with hundreds of redundancies in prospect.
McAvoy: "This situation results from government incompetence"
He blamed higher national insurance payments, larger employer contributions to teachers' pensions and changes to pay and conditions.
The government has claimed £500m earmarked for schools is being held back by local authorities, which are using the money for other services.
But Mr McAvoy, told a press briefing at the NUT's annual conference in Harrogate, North Yorkshire, the situation was foreseeable and ministers had failed to act.
He said: "This situation results from government incompetence.
"We want the government to accept it is wrong and make the changes needed to ensure schools can continue to provide the high quality education they are providing at the moment."
A survey commissioned by the NUT found schools needed between 8% and 14% to maintain current services.
The government has promised an extra 3.2% in funding for each pupil.
The NUT says this will not be enough, given the increased cost of pensions, National Insurance and changes to working conditions, aimed at providing more teacher time for marking and lesson preparation.
It estimates some schools will face funding shortfalls of up to £200,000.
Mr McAvoy said: "We are not interested in an argument between the government and employers.
"The test is whether the schools have the money. Plainly, they do not.
He added: "The government has not budgeted adequately for the needs of schools.
"It is giving with one hand and taking away with the other."
The conference will debate a motion condemning the government's handling of school finances on Sunday.