Schools are spending tens of thousands of pounds more a year to meet rising costs of contracts with private firms.
These Private Finance Initiative (PFI) schools are locked into 25- to 30-year contracts in which charges rise more than at other schools.
One school said it was spending thousands of pounds a year to keep its playing-field grass below 2.5cm (1in), as the "rigid" contract demanded.
PFI investors say the contracts give long-term value for taxpayers' money.
Middlefield Primary in Speke, Liverpool, opened after the local authority entered a PFI agreement for new school buildings.
Head teacher David Potter says nearly 20% of the school's entire budget is now spent on meeting the terms of the PFI contract - squeezing what he can spend on classroom staff.
The school has to pay the PFI company for its day-to-day maintenance, catering and cleaning, which will cost more than £470,000 ($600,000) this year - a rise of more than £151,000 since 2021.
And what Mr Potter says is one of many "rigid" details stipulates the grass must not grow higher than 2.5cm, even in the winter when the playing field is hardly used.
"Come rain or shine every week, the grounds maintenance team come out and they cut this field," he says.
"We should have the freedom to say, actually, we think we can do without."
