A headteachers' union has warned that the Department for Education “doesn’t have the right data” to accurately calculate what individual schools need to cover the cost of teachers' pay rises.
The NAHT says there will be “winners and losers” in tomorrow’s funding allocations, which are being made from a DfE £105 million pay grant .
The union's funding specialist, Ian Hartwright, said schools with more experienced and expensive staff would lose out in the allocations.
Mr Hartwright said: “When you apply the pay grant, the DfE doesn’t have the accurate salary information for every staff member in every school.
"If they were going to get it absolutely right, they would need to know how everybody was paid. The DfE is using the best and most reliable data but it’s a complex picture.”
Mr Hartwright also said some schools would struggle to fund their share of the pay award (2 per cent of the 2.75 per cent) and that schools may have to cut staff, including TAs, as well as cut back on “office functions”.
He said: “Some of our members tell us they can’t afford the 2 per cent because they’re in dire funding straits. It would be up to the governors or the [multi-academy trust board] to decide whether to pay it, but we would always recommend schools should pay the full 2.75 per cent.”
Meanwhile, the NEU teaching union said some teachers still hadn’t received last year’s pay award.
Mary Bousted, joint general secretary, said: “We are taking steps this year to ensure that every teacher knows they are entitled to a pay rise and every teacher receives it.”
The individual school funding allocations will be published on the DfE website from 10.30am, along with school-by-school breakdowns of how £850 million will be shared to cover an increase in school pension contributions for teachers.
Headteacher Jules White of the Worth Less? school funding campaign said: "Any salary rise for teachers is, of course, welcome.
"The issue with the current pay grant is that it only covers 0.75 per cent of the total award. The other 2 per cent is taken straight from school budgets.
"As ever, the DfE overlooks these substantial extra costs and the real-term effects it has on our budgets.
"Looming in the future is how any proposed significant pay awards will be funded. While teachers should be paid more to help with our recruitment crisis, schools and our pupils will be shortchanged if any such awards are not fully funded.
"Most heads I speak to are extremely worried that recent funding announcements by the government will be swallowed up by new pay awards."
Julia Harnden, funding specialist at the Association of School and College Leaders, said: “Schools will need to check how closely their allocations meet increased pension contributions.
"The grant should cover the whole increase and if there is any shortfall then schools can bid into a supplementary fund to make up the difference.”
The DfE has been contacted for comment.