More than 1,000 local authority councillors have signed a letter urging the government to increase school funding.
The letter from the NEU teaching union to education secretary Damian Hinds is due to be handed to the Department for Education this afternoon.
It came after Mr Hinds last month told the annual conference of the Association of School and College Leaders he had “heard the message loud and clear on school funding”.
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In the letter, 1,115 councillors said the funding crisis has seen growing budget deficits, cuts in teaching staff, reductions in some subject areas and poorer education.
It says: “The funding crisis has become so overwhelming that according to the Education Policy Institute, almost a third of all council-run secondary schools are now in deficit, and eight in ten academies are in deficit according to last year's Kreston UK report.
“Many schools are now desperately overwhelmed, as more and more students are competing for fewer and fewer resources. Compounded by biting cuts to local council services, in addition to the teacher recruitment and retention crisis, the current settlement is not tenable.”
Councillors urged ministers to reverse funding cuts made since 2010 and better fund SEND provision.
A group of unions in the School Cuts coalition last month put the shortfall in school budgets over the past three years at £5.4bn, and said 91 per cent of schools in England had been affected.
Brent’s Jumbo Chan, NEU Councillors Network joint convenor, said: “The government must heed the calls of locally-elected representatives who can see first-hand the havoc school cuts – compounded by biting cuts to precious local government funding – are wreaking on many young people.”
Joint convenor Maggie Browning, a Southwark councillor, said: “Increasingly, tighter funds mean schools across the country are narrowing their curriculum and cutting subjects like drama and art, which is a travesty.
“Teachers’ workloads have become unsustainable as they are asked to do more and more with less, including larger class sizes and fuller timetables with less support.
“This is fueling the recruitment and retention crisis across the country, with one in three teachers leaving in the first five years of joining the profession.”