Schools in an area of Northampton would each see an average funding drop of more than £140,000 a year if the Conservatives are re-elected this week, a national teachers' union has claimed.
In an attack against the Tories days before the election, the National Union of Teachers (NUT) has updated a national website showing the extent of school cuts in local areas to reflect 2017 party manifestos.
The NUT says the figures build on recent analysis by the Institute of Fiscal Studies and take into account growing school age population.
In Northampton South per pupil spending will decrease by £328 per head by 2022, the union claims, and £140,056 per school if Theresa May's party is re-elected.
On the other hand, Labour's public service-heavy manifesto would see spending increase by £116 per pupil and £49,472 per school.
A Lib Dem victory would result in a £172 reduction per pupil and a £73,362 drop per school.
Northamptonshire division secretary for the NUT, Stuart Coe, said: "Every parent needs to know what the parties are planning to invest in education.
"Candidates should be held to account for their parties' stance to education. Without sufficient funds schools will be forced to drop subjects from the curriculum, increase class sizes or offer less individual attention to pupils. I urge everyone to vote for education."
The Conservative manifesto commits £1 billion extra funding for education each year until 2022. But the NUT says this would result in an £8.9 billion real terms cut, when taking into account inflation and growing pupil numbers, between now and then.
The Labour manifesto commitment will mean an extra £4.8billion a year funding for schools and the Lib Dems a £2.2 billion funding boost, which would give protection on 2017/18 funding levels.
However, Northampton South candidate Andrew Lewer has disputed the NUT figures
He said: "No school will have its budget cut and the schools budget will rise to £45 billion, the highest on record.
"The NUT may say they are not affiliated to the Labour party but they are the most left-wing of all the teaching unions and many of their prominent members are supporters of Corbyn and his magic money tree."