Research by the Institute for Fiscal Studies says schools will be hit by a real-terms cut of 'at least 7 per cent'.
School budgets are being pushed to "breaking point" by the largest drop in real-terms funding since "at least the late 1970s", headteachers' leaders have warned.
A new analysis of school funding by the respected thinktank the Institute for Fiscal Studies (IFS) has revealed that spending per pupil is expected to fall by at least 7 per cent by the end of this Parliament.
The tougher spending round will make introducing a national funding formula (NFF) more challenging, the thinktank said.
Last month, chancellor George Osborne pledged an extra £500 million to "speed up" the introduction of a new formula in his Budget speech.
Luke Sibieta, a researcher at the IFS and author of the report, said the introduction of a new funding formula would be "one of the most radical shake-ups of school funding in at least the past 30 years".
"Replacing 152 different formulae with one single, simple formula will inevitably lead to substantial changes in funding across schools and, for good or bad, will almost completely remove local authorities from the school funding system," Mr Sibieta said.
In light of the report, heads’ and teachers’ leaders warned the government that "redistributing money will not be enough", adding that the drop in spending was having a "significant impact" on schools.
Investment 'urgently needed'
Malcolm Trobe, interim general secretary of the Association of School and College Leaders, warned that "greater investment is urgently needed in education to help ensure all young people receive the best possible start in life".
"The government’s plan to introduce a new funding formula to address wide geographical variations in school funding is certainly needed but redistributing money is not in itself enough," he added.
Russell Hobby, general secretary of the NAHT headteachers’ union, added that "with flat cash education spending at a time of rising costs, school budgets are being pushed to breaking point".
The ATL teaching union said it was concerned the new funding formula would take money away from schools.
"The government’s NFF proposals will lead to funding losers and winners among schools, but rather than cut the funding to some schools, we urge the government to level up funding,” Nansi Ellis, ATL assistant general secretary, said.