State schools in England are facing budget cuts totalling £3bn by 2019-20, an average of 8% each.
The scale of the funding crisis, forecast by Tribune last month, was confirmed by an analysis from the National Audit Office (NAO).
Around 60% of secondary schools already have deficits, and the watchdogs warned that can only grow over the next three years.
The Department for Education has launched a new funding formula, which will see 10,000 schools gaining money and similar numbers losing.
The Education Secretary Justine Greening is aiming to ease the impact of cuts in central London and previously under-funded areas such as Barnsley and Plymouth.
But critics warned that the funding re-jig will mean a greater squeeze elsewhere because it will involve reallocations of funding rather than extra investment overall.
The NAO report said that schools are not prepared for the “scale and pace” of the cuts facing them. Funding is not keeping pace with increased pupil numbers and rising costs of national insurance and pension contributions – and the budget gap will have reached £3bn by the end of the decade.
The overall budget is protected against inflation, but the NAO said that rising numbers of pupils will mean schools will face cuts in real-terms per-pupil income. The report forecast shortfalls averaging £326,000 by 2020.
Five head teachers’ and teachers’ unions issued a joint statement saying schools face the “biggest real-terms cuts in a generation”.
Malcolm Trobe, head of the Association of School and College Leaders, said: “We are deeply concerned that the life chances of young people are being put at risk by the government’s under-funding of education.”
Ann Lyons, headteacher at St John Fisher Catholic Primary School in north west London,said her school is already struggling to maintain services and is cutting activities. She said: “We are finding that we can’t increase the staffing in line with the pupil numbers. So class sizes have got to a real maximum. We’ve been relatively well protected but we are now at the stage we’re at breaking point and the only way some schools are going to manage this significant cut in real terms is through staff cuts – and that’s going to add to workload.”
Sean Maher, head teacher of Richard Challoner School in Kingston, said he feared that the good work of teachers, students and parents was masking a crisis that was happening in education across the country. He added: “The problem is that no school, no teacher, wants to let their children to fail or their standards or expectations to drop. “So teachers strive harder, support staff plug gaps and leaders try to sleep at night whilst trying to solve a problem that is not of their making.” Teachers are “utterly despondent and dismayed about finance and teacher recruitment”.
In the autumn almost every state school head in the local authority had written to the Prime Minister Theresa May in the autumn warning of the “dire financial position”. A round-robin letter from more than 250 heads said: “Schools are struggling to function adequately on a day-to-day basis, and, in addition, we are severely hampered in our ability to recruit and retain staff, work with reasonable teacher-pupil ratios and to buy basic equipment.”
Shadow education secretary Angela Rayner said: “This is the reality: the Tories are cutting school budgets. All we have seen from this government is six years of turmoil in our schools and nothing to show for it.”