A third of schools have not received the extra money the Government promised all heads this year and more than one in 10 have actually seen funding fall.

The figures, which raise doubts about whether Labour really has avoided a repeat of last year’s school funding crisis, are expected to be released today by the National Association of Head Teachers as it opens its annual conference in Cardiff.

Its survey of 806 schools in 137 local authorities shows that 34 per cent received less than the 4 per cent per pupil increase, promised by the Government in October to schools where pupil numbers fell or stayed the same.

Schools with rising rolls were promised a 3.4 per cent per pupil increase, but only 28.8 per cent of those surveyed by the NAHT said they received even this.

Nearly 11 per cent, mainly schools with rising rolls, actually received less per pupil than last year. Some reported percentage drops in double digits, including a North Yorkshire school where funding per pupil fell by a third.

Conversely 27 per cent of schools received increases of 8 per cent or more per pupil, with some double digit rises including a reported 52 per cent increase at a Durham school.

Heads at the conference will also debate the workforce agreement. Two separate conference motions have been tabled calling for the NAHT to withdraw from the agreement unless the Government provides adequate funding, one setting a deadline of August 31.

The NAHT repeatedly threatened to pull out last year over the funding crisis. But its national council opted for a change of tactics in January, voting that it was better to fight for members’ interests by staying on board.

The council is likely to propose its own conference motion, backing that decision. But there is growing evidence of grassroots reservations about the agreement within the NAHT.

Its representatives in the London boroughs of Lambeth and Newham have already signed local agreements with other unions overturning the workforce deal and stating that classroom assistants should not teach whole classes.

David Hart, NAHT general secretary, said pulling out would not make a blind bit of difference. He is expected to use his speech on Sunday to say that the performance pay deal and the new Office for Standards in Education inspection framework will mean that “good” will replace “satisfactory” as the benchmark against which all teachers will be assessed.

“The classroom teacher organisations have signed up to a deal that says only good teachers reach UP3 (the top of the upper pay scale). This means that satisfactory teachers do not qualify,” he is expected to say.

He will add that whether the classroom teachers like it or not, “satisfactory is becoming no longer good enough”.

Mr Hart will also say that heads are being “hung out to dry” by education authorities that do not back them when they attempt to sack incompetent teachers.

Charles Kennedy, the Liberal Democrat leader, is expected to use his speech to the conference on Monday to call for skilled teachers and school buildings made redundant by falling primary rolls to be used to create one-stop early-years centres.

He will also say that every child has the right to be taught by a qualified teacher and that classroom assistants are no substitute.