Budget cuts could see grammar schools ask parents for hundreds of pounds a year, head teachers have warned.
The Grammar School Heads Association (GSHA) said families could be asked for up to £40 a month to ensure teaching standards do not fall when new school funding reforms are introduced.
Conservative MPs have called for the government to review the “unacceptable” changes which could leave some schools forced to cut facilities or switch off heating to keep costs down, the Press Association reported.
Tim Gartside, head of Altrincham Grammar School for Boys, said he was considering asking parents for voluntary contributions - as are many of his colleagues.
He told BBC Radio 4’s Today programme: “We have a choice, I suppose. Either reduce the curriculum, increase the class size or go to parents and say we need to ask you for a contribution in order to be able to make the school operate as it has done before.”
Education Secretary Justine Greening announced the new national funding formula in December, which will target schools with additional needs such as deprivation.
It is estimated that the changes, to be introduced between 2018 and 2019, will mean more than 10,000 schools gain funding.
But unions have warned that 98% of schools will face a real-term reduction, with an average loss of £477 per secondary school student.
The GSHA has calculated that almost two-thirds (63%) of grammar schools will lose money, adding that the majority already receive less funding than is considered viable to run a school.
Conservative Fiona Bruce told the Today programme: “All my senior school head teachers and many of my junior heads are saying that the way this formula is calculated will leave them with no choice but to actually effectively reduce teaching standards in their schools.”
The Congleton MP said schools were looking at leaving teaching posts vacant, reducing curriculum options, closing sixth forms and special needs units, and switching off the heating as ways of saving money.
“This is unacceptable, this is not fair funding,” Bruce added.
A Department for Education spokesperson defended the reforms, calling the current method of funding “unfair, opaque and outdated”.
“We are going to end the historic post code lottery in school funding,” they said.
“Funding every child fairly and according to their specific needs sits at the heart of delivering the Government’s pledge to build a country that works for everyone, not just the privileged few.
“We recognise that schools are facing cost pressures, which is why we will continue to provide advice and support to help them use their funding in cost effective ways, including improving the way they buy goods and services, so they get the best possible value for their pupils.”