Schools in England are preparing to move to class sizes of as many as 60 children from September to deal with a funding crisis that headteachers say will force them to cut staff. The government insists that there is still room in school budgets to cover the 4.5% pay offer that teachers overwhelmingly rejected last month, as well as rising costs. But angry headteachers have warned that next year they will reach the brink, with no option but to cut staff and increase class sizes. Some schools are also considering shortening the school day to cut teaching time, with one academy leader warning that another year of underfunding would force many schools into a four-day week. A senior leader in a large multi-academy trust, speaking anonymously to avoid alarming parents, said: “We will be forced to collapse classes. I’m looking at going from 10 sets to eight in maths and English, with a top set of up to 50 or even 60 kids in a big space.” The leader said they were already having to “double up classes” to cover absences, and this would get worse. One of their secondary academies had 15 staff off last week, with stress-related illness noticeably on the rise. “The senior team has been teaching 100 kids a time in the hall to relieve pressure on teachers,” he said. “Cover lessons make behaviour worse.” As well as cutting less popular sixth-form subjects and increasing A-level class sizes – in some cases to twice the optimal number of pupils – he is considering cutting costs by starting the school day late or finishing early once a week. He said: “If we have another year of this underfunding, by next year I think you’ll have lots of schools going to a four-day week because they can’t afford to teach for five.” He has just voted to strike for the first time. “Not being funded has happened so many times,” he said. “I’m fed up with being lied to by the government.” Education secretary Gillian Keegan insisted last week that schools could afford a 4.5% average teacher pay rise with just £90m of additional funding, after the government committed £2bn for each of the next two years in last year’s autumn statement. But headteachers and unions say the extra funding has been hoovered up by soaring energy bills, largely unfunded pay rises for teachers and support staff last summer, and increased costs for everything from school meals to exercise books, leaving many schools facing staff cuts next year. James Bowen, director of policy at the National Association of Head Teachers union, said: “School leaders are angry. They are being told this is all affordable, but there is no money left. Our members say it’s been spent on keeping their heads above water.” Dave McPartlin, head of Flakefleet primary school in Lancashire, said: “With a 4.5% pay rise and no extra money, we would be in deficit, so staff would have to go. We already can’t afford to replace some great staff who are leaving.” The head of a primary academy, who asked to remain anonymous, said: “For our older children, class sizes will have to increase. That means we won’t meet their needs fully.” Jonny Uttley, chief executive of Teal multi-academy trust in Yorkshire, said that any cuts to teacher numbers next year would hit the poorest children hardest. “We rightly focus on disadvantaged children, and the single biggest factor in their success is the quality of the teacher in front of them.” Suzanne Best, head of Great Kingshill Church of England primary school in High Wycombe, said: “If support staff continue to leave, we will not be able to replace them. Is that the right decision for the children? Absolutely not.” The DfE said: “Since this government took office, there are now more than 24,000 more teachers in our schools, and our secondary schools have an average of 22 pupils per class.”