Schools are being forced to axe GCSE and A-Level courses in a desperate attempt to tackle severe budget pressures, headteachers have warned.
Design and technology, languages and arts subjects are all being dropped as schools face a serious funding crisis, according to a Association of School and College Leaders (ASCL) report.
A poll of more than 1,000 members found that class sizes are swelling and after-school clubs and trips are being scrapped as headteachers struggle to cope, the Press Association reported.
The government has argued that school funding it at its highest ever level.
But ASCL interim general secretary Malcolm Trobe said school leaders are being forced to make “impossible choices”.
The survey found that 72% of headteachers whose schools teach 14 to 16-year-olds have had to to cut GCSE or vocational courses.
Almost eight in 10 (79%) with sixth form students have had to axe subjects.
The most common GCSE subject to be axed was design and technology (44%), followed by performing arts (26%), music (18%) and German (18%).
Design and technology courses were also most likely to be dropped at A Level (41%), with music (39%) and German (37%) also facing the chop.
Rising class sizes was flagged as another major concern for school leaders in the survey, with 82% saying they have had to expand the number of pupils in each class.
One average, headteachers said their largest class is 33 pupils - but one in eight (12%) that students at their schools are being taught in classes of 35 or more.
One school leader told the union: “Through no fault of their own, students will have restricted subject choices, in larger class sizes with less pastoral support, whilst still being expected to perform at the highest of standards - nonsense!”
Another added: “Increasing numbers of students are taught in badly maintained and leaking buildings. They are using out-of-date IT equipment which frustrates them as they tend to have the latest computers and tablets at home.”
The vast majority - 95% - said that their school has cut back on support services, including equipment such as books, special needs support, IT and mental health support.
Over two-thirds (68%) said they have had to scrap activities such as trips, visits and clubs.
Trobe said: “The survey shows the impossible choices school leaders are having to make.
“Reduced budgets means fewer staff and, with fewer staff, class sizes have to increase. Schools cannot sustain the level of support they provide to pupils, or the range of subject options and enrichment activities.”
He added: “Unless the government invests more in the education system, there will be a significant impact on the lives and life chances of young people.”
The ASCL argues that the funding crisis is caused by rising costs such as employer National Insurance and pension contributions, without additional funding from the government to pay for them.
The union argues the situation will be made worse when the apprenticeship levy is introduced next month.
A recent report by the National Audit Office has warned that schools will have to save £3 billion by 2019/20.
A Department for Education spokeswoman said: “The Government has protected the core schools budget in real terms since 2010, with school funding at its highest level on record at more than £40 billion in 2016-17.
“But the system for distributing that funding across the country is unfair, opaque and outdated.
“We are going to end the historic postcode lottery in school funding and, under the proposed national schools funding formula, more than half of England’s schools will receive a cash boost.
“We recognise that schools are facing cost pressures, which is why we will continue to provide support to help them use their funding in cost-effective ways, including improving the way they buy goods and services so they get the best possible value.”