Nearly half of the NUT's school representatives have reported cuts to teaching posts owing to funding pressures, a new survey reveals.
And three-quarters (74 per cent) of respondents have already heard their headteacher express concerns over funding, according to the research from the union.
The survey of more than 400 NUT representatives shows that 67 per cent have seen or expect to see reduced funds for books and resources in their schools. Fifty-nine per cent have already seen or are expecting increased class sizes, and 50 per cent have already seen or expect cuts to SEN and EAL provision.
Almost half (47 per cent) say teaching posts have either already been cut or are expected to be cut in their schools, while over half (57 per cent) report cuts in classroom-related support staff posts.
The research finds that most job losses for teachers are being achieved through natural wastage, non-filling of vacancies and voluntary measures, rather than compulsory redundancies.
It reveals that 45 per cent of respondents think teachers are more likely to be paying more towards classroom resources than previously, while 21 per cent say funding cuts will lead to fewer activities being available to pupils.
Last month, the Institute for Fiscal Studies (IFS) warned that schools face the first real-term cuts since the 1990s, with cuts of up to 8 per cent in the next Parliament.
As the NUT released its research, headteachers' union the NAHT wrote an open letter to education secretary Nicky Morgan reinforcing headteachers' concerns about funding ahead of the government's spending review next week.
In the letter, NAHT general secretary Russell Hobby wrote: "For too long, education has been seen as a cost; in fact, education is an investment, in both children and society as a whole.
“We would urge you, in conversations with chancellor George Osborne, to call for progressive funding arrangements for education. It’s time that funding reflects the true realities on the ground; something our members call for on a daily basis."
Earlier this month, the NAHT released a report showing that nearly two-thirds of school leaders are making "significant" cuts or are dipping into reserves to stave off deficits.
Today the NUT is lobbying MPs, in person and by email, about the impact of education funding cuts ahead of the spending review.
Christine Blower, general secretary of the NUT, said: “The government is failing in its duty to provide children and young people in England with an education that is properly funded and gives all children the start in life they deserve.
“Parents and carers will be utterly dismayed to see the impact government funding policy is having on their children’s education and their future prospects.
“On top of this, the government is planning a review that will increase funding in some areas of the country simply by taking it from other areas of the country, not by providing the increased funding that some parts of the country sorely need.
“Government ministers and MPs generally all need to take note of the consequences of the decisions they are taking on education funding. Unless there is a change of direction, the government will be failing this generation of students.”
A spokesman for the Department for Education responded to the NUT survey: “This government is taking the difficult decisions necessary to ensure that the schools budget is protected and will continue to rise as pupil numbers increase. This is a key part of our commitment to extending opportunity and delivering educational excellence everywhere."