The Conservative Party's school spending plans would lead to a real-terms cut of nearly 3 per cent - taking funding back to 2010 levels - according to a respected thinktank.
The Tory manifesto said its plan to spend an extra £4 billion by 2022 on schools represented "more than a real terms increase for every year of the parliament".
But the Institute for Fiscal Studies has calculated that the pledge would equate to a real-terms cut in spending per pupil of 2.8 per cent between 2017-18 and 2021-22, or 7 per cent using 2015-16 as the starting point.
The figures take into account rising pupil numbers as well as the increased costs facing schools, such as increased pension contributions.
School spending per pupil as it stands is set for its biggest fall in 30 years, amounting to a 7 per cent real-terms cut between 2015-16 and 2021-22, the IFS has said.
In contrast, Labour would increase real-terms spending by 6 per cent between 2017-18 and 2021-22, while the Liberal Democrats would keep spending per pupil frozen in real-terms during the same period, according to the IFS.
By the end of the next parliament, Labour's plans would see each secondary pupil attracting £6,500 per year, compared with about £6,000 under the Conservatives' plans.
Luke Sibieta, the IFS associate director who co-authored today's analysis 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 per cent 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 per cent real terms fall in spending per pupil over the parliament, taking it back to its level in 2010.”
He told Tes: "This equates to a slightly slower path of real-terms cuts to school spending per pupil as compared with current plans - 1.7 per cent per year on average under current plans up to 2019–20 compared with 1.2 per cent per year under the new Conservative plans up to 2021–22."
However, these figures do not take account of the potential for the 1 per cent cap on public sector pay increases to be removed.
Increasing public sector pay in line with private sector earnings - which Labour supports - could increase schools' costs by £2.8 billion in 2021-22, IFS researchers have found.
The Lib Dems want to increase pay in line with inflation, which could cost schools £1.6 billion.
National funding formula
All the parties have promised that no school will lose out under the planned National Funding Formula for schools, which the IFS has said would cost an additional £350 million a year.
However, at some point, whichever party is in power will need to remove the funding protections, in order to move all schools onto the formula.
The IFS paper published today said: "The striking result is that with a cash-terms freeze in overall spending and the additional protections that have been announced only 40 per cent of schools are on formula in 2019–20."
It adds: "Such a reform necessarily creates relative winners and losers, but with no overall growth in funding the reform must create absolute losers to transfer the additional funding to those that gain."