A poll of more than 1,000 secondary headteachers and senior leaders, carried out by the Association of School and College Leaders (ASCL), lays bare the financial pressures faced by schools across the country.
More than 80 per cent of respondents said their schools would not have enough funding to meet "essential needs" over the next 12 months; almost 90 per cent said this would have a detrimental effect on the education their schools were able to provide. Some could even be forced to reduce opening hours to avoid insolvency, the ASCL warned.
Fifty-three per cent of leaders said they were planning to make redundancies in the coming year, with 67 per cent proposing to reduce the number of courses on offer and 71 per cent looking to increase class sizes to balance the books. Some 67 per cent said they were considering cutting expenditure on resources such as ICT equipment and books, while 62 per cent said they expected to reduce CPD budgets.
When asked how grave their financial situation would be next year, almost 70 per cent said either "critical" or "very serious". Just 1 per cent believed that their school would be "fine".
Speaking ahead of the ASCL's annual conference, which starts in London today, deputy general secretary Malcolm Trobe said several factors had combined to leave schools facing a 4-5 per cent cut in their budgets for 2015-16.
"The situation is extremely difficult," he said. "We've got real funding pressures in 2015 and 2016 from inflation, unfunded pay rises, an increase in employers' pension contributions from September, an increase in National Insurance contributions from next April and, for academies, a reduction in the education services grant."
At current funding levels, Balcarras School in Cheltenham faces insolvency by the end of 2017-18, according to headteacher Chris Healy. The school has to make savings of pound;250,000 in 2015-16 to avoid "financial disaster".
"We're about as efficient as we can be," he said. "We can't find further ways to reduce our costs, we're just hoping for the best. The only way we can make ends meet is if the government puts more money in. We're a very successful and well-managed school, but we're still heading for disaster financially."
Brendan Wall, headteacher of St Simon Stock Catholic School in Maidstone, Kent, said that the long-term outlook for his school was "very bleak" and that he was bracing himself for efficiency savings.
"The knock-on effect will be cuts to significant budget areas such as staff development programmes at a time when the government is introducing changes to the curriculum," he said. "Books and equipment and maintenance may take a knock as well. I'm concerned that teachers may not be as well prepared for the curriculum changes as they would otherwise be.
"The longer-term picture looks very bleak. The money within the system doesn't seem sufficient to meet the demands of the increasing number of students coming into the system."
Another school facing increasing financial pressure is Haywood Academy in Stoke-on-Trent. Headteacher Carl Ward said it had made savings since becoming part of a multi-academy trust, and now shared its human resources, finance functions and professional development costs with other schools.
"The schools I'm most worried about at the moment are those that aren't working in partnerships to make these savings," he added. "But in 12 months' time we could max out on saving. So unless there's extra funding, we'll be affected [by cuts] too."
Many of the school leaders surveyed said they had already been forced to make significant savings in the current academic year; 35 per cent had made redundancies and 74 per cent had not replaced support staff who had left. A further 41 per cent had opted to cut the number of senior leadership posts at their schools.
A Department for Education spokeswoman said the government had protected the schools budget and was committed to introducing a national funding formula for schools.
"We have also announced an extra pound;390 million for schools, the biggest step toward fairer schools funding in a decade," she added. "The pupil premium - which is worth pound;2.5 billion this year to schools - is also ensuring teachers continue to have the resources they need to give all pupils the best possible start at school, regardless of their background."
`We can't possibly manage'
Balcarras School in Cheltenham sees itself as entrepreneurial: it raises pound;50,000 a year by selling consultancy services to other schools and its catering service also makes a pound;50,000 annual profit. It has been praised by schools minister David Laws for reducing the attainment gap between pupils eligible for free school meals and their classmates.
But headteacher Chris Healy is planning a long list of cuts as a result of reductions to post-16 funding, as well as rising pay, pensions and National Insurance contributions.
These measures include reduced spending on ICT, lunchtime supervision, administrative staff, cleaning, building maintenance and music tuition. He is also being forced to replace experienced departing teaching staff with newly qualified teachers and is considering asking sixth-formers to cover their own AS-level exam fees.
"We've got all these additional costs that we can't possibly manage in our budget," he says. "We're hoping it will have as little impact as possible on students' outcomes, but the only way the education of pupils isn't going to be dramatically damaged is if we get more money."