Schools are being forced to ask parents for money due to unacceptable cuts, according to a mother at a rally about funding.
Hundreds of parents, children and teachers have staged a protest in central London against cuts to school funding as part of a campaign called Fair Funding For All Schools.
Jo Yurky, co-founder of the campaign, said she is aware of schools that have asked parents if they would be willing to make monthly payments of £20 to £50 or a one-off payment of £250.
The mother of two girls, who lives in Muswell Hill, North London, said: "I've discovered that schools near me were asking parents for money on a direct debit basis."
She said the money was going into a fund to "keep the school afloat", adding: "Money was so tight that they couldn't balance their books unless they asked parents to give a regular donation on a monthly basis."
Ms Yurky said it is voluntary but particular amounts are being suggested.
She said she was aware of another school which wrote to parents and suggested "a minimum amount could be £250" as a one-off payment.
She said parents are not angry at the schools, explaining: "Our issue is not with the schools for doing that. Our issue is why is there a problem? This is not a sustainable way to fund our schools. There is clearly a financial problem in our schools.
"And this is not a long-term solution to that."
Ms Yurky was shocked into action on hearing that the local secondary school was increasing class sizes because of funding constraints when she was at the open day.
She told how the head teacher there said class sizes would be going up "because money's tight".
Ms Yurky earlier said: "Parents are deeply unhappy about the Government's failure to adequately address the funding crisis facing our schools.
"Whilst the Government is busy saying nothing, damaging cuts are being made to our children's education. This is unacceptable.
"We will continue to apply pressure to force the Government to provide an urgent remedy.
"We want increased investment in our schools so that our young people have the skills and knowledge they need and so that our future economy can reach its full potential."
A banner in Parliament Square, where the crowd gathered, carried the hashtag #schoolsjustwannahavefunds.
It also included a letter directed at Secretary for Education Justine Greening which said: "Our schools are facing a financial crisis.
"Please act now to ensure that our schools have the funding they need to continue providing high quality education for our children and young people."
Children held banners with messages such as "Up with schools, down with cuts" and "(Theresa) May I have a future?"
The Fair Funding For All Schools campaign is calling on the Government to immediately reverse cuts to school budgets that have taken place since 2015 and protect per pupil funding in real terms over the lifetime of this parliament.
It also calls on the Government to provide the additional funding needed to implement a school funding formula that increases funding for schools in comparatively poorly funded areas of England without cutting funding per pupil for schools in any other part of the country, so that no school loses out.
The campaign said analysis by the Institute for Fiscal Studies shows that under current government spending plans, including the additional £4bn announced in the Conservative Party election manifesto, spending per pupil is set to decline by a further 3% from 2017 to 2022, making a total 7% reduction from 2015.
Alex Kenny, 57, an English teacher at a secondary school in east London, said the school he works in has made decisions to cut back on school trips, adding that other schools are cutting back on people coming in to teach children art, drama and PE.
"So there are all kinds of things that enrich the lives of young people that schools are now stopping," he said.
Mr Kenny said he knows of one children's writer who, in an average year, would have visited 150 schools but it is now down to about 30 or 40 schools.