Schools could still be left out of pocket by a Conservative pledge to boost education spending by £4 billion over the next five years, a leading economic think-tank has said.
Under the party's plans, school budgets in England could face a real-terms cut of almost 3% by 2021/22, according to the Institute for Fiscal Studies (IFS).
In a new paper examining each of the main political parties proposals for school spending, the IFS also calculated that Labour's plans would leave per pupil spending 6% higher in real terms over the same five year period (2017/18 to 2021/22).
And the Liberal Democrats' plans would see per pupil spending protected in real terms at the 2017/18 level.
In their General Election manifestos, all three of the main political parties pledge to address education funding, with each setting out a different method which it says will increase money for schools.
It comes amid continued concerns from school leaders, teachers and parents about a growing squeeze on school budgets.
The Conservative manifesto says: "We will increase the overall schools budget by £4 billion by 2022, representing more than a real terms increase for every year of the parliament."
According to the IFS analysis, once inflation and growth in student numbers is taken into account, these plans would imply a real terms fall in spending per pupil of 2.8% between now and 2021/22.
This rises to a 7% reduction by 2021/22 once the cuts schools have faced over the last two years are taken into account.
Labour has pledged to reverse real-terms cuts since 2015, and protect per pupil spending in real terms over the next parliament.
This would mean a 6% increase in per pupil spending over the next five years, and leave per pupil spending 1.6% higher in 2021/22 than in 2015/16.
The Liberal Democrats have set out a five-year package that includes protecting per pupil funding in real terms.
Under this commitment, spending per pupil would be frozen in real terms over the next parliament, the IFS says.
IFS associate director Luke Sibieta said: "The commitments made by each of the main parties would imply quite different paths for school spending in the next parliament.
"Labour would increase spending per pupil by around 6% after inflation over the course of the parliament, taking it to just above its previous historic high in 2015.
"Proposals from the Conservatives would lead to a near 3% real terms fall in spending per pupil over the parliament, taking it back to its 2010 level."
Schools Minister Nick Gibb said: "Jeremy Corbyn can't deliver any of his promises on school spending – this analysis shows his numbers categorically do not add up and he is too much of a shambles to negotiate a Brexit deal that works for Britain."
He added: "We will increase the overall schools budget by £4 billion by 2022 – a real terms rise for every year of the Parliament compared to current spending plans – and ensure that no school has its budget cut as a result of a fair funding formula."
Angela Rayner, Labour's Shadow Education Secretary, said: "There is now no doubt about what Tory plans mean for education - our schools will see their budgets cut.
"And head teachers have warned us what the consequences will be for parents and pupils: fewer teachers, larger classes, a narrower curriculum, or even a shorter school week."
Sarah Olney, Liberal Democrat Shadow Education Secretary: "Under the Conservatives our schools are in crisis, our children are being taught in overcrowded classes by overworked teachers.
"While funding per pupil is set to see the biggest cuts in a generation, billions of pounds are being spent on divisive plans to expand grammars and free schools in areas where they aren't needed."