Schools are six figures in the red, says the NAHT

David Hart, general secretary of the National Association of Head Teachers (NAHT), said schools lacked funds to implement the reforms.

In January, all major teaching unions, except the National Union of Teachers, agreed to a remodelling of the working week.

This will free up half a day a week for marking and lesson preparation, leaving more duties to assistants.

Schools say this will impose a greater burden on already stretched resources.

'Undeliverable'

On top of this, they have been told to raise their contributions to teachers' pension funds, while employer National Insurance rates are set to rise in the forthcoming Budget.

The NAHT says some schools are already six figures in the red.

Mr Hart said: "The funding situation for many schools is very serious.

"We cannot divorce the lack of resources from the cost of implementing the agreement as some other signatories would like to do.

"The NAHT strongly supports the principles behind the agreement, but not at any price and certainly not at the price of teachers and support staff jobs.

"That is why we cannot agree the contract changes while the issue of funding for this and subsequent years has not been resolved to our satisfaction."

Earlier this week the government announced an extra �28m for schools in 36 local education authorities in England.

Schools minister David Miliband promised to listen to "sensible representations about any major new system".

But Mr Hart said the threat of teacher redundancies had not been averted.

He added: "The state of school budgets makes the agreement undeliverable in many schools.

"NAHT will continue to fight its corner in the workload reduction negotiations.

"But any attempt to ram through contractual changes, that are not funded properly, will only drive schools into further financial difficulty and damage standards."