Private schools will be asked to help set the criteria used to determine whether they can remain charities if the Government presses ahead with its charities bill.
The Charity Commission, which will carry out checks when the bill is approved by Parliament, says it will consult the independent sector before it establishes the benchmarks.
Factors likely to be considered include public access to school buildings and land and whether the schools provide bursaries and scholarships for less well-off pupils, a spokeswoman said.
The draft charities bill published last week proposes that private schools should lose their charitable status and all the associated tax benefits if they cannot pass a "public benefit" test.
But private schools are confident that they will be able to prove they are of public benefit and have been assured by the Government that they are likely to remain charities. Fiona Mactaggart, the Home Office minister, said the bill was unlikely to affect private schools, even high-charging institutions like Eton where annual fees are more than pound;21,000.
The Independent Schools Council estimates that its 1,280 member schools save the taxpayer pound;2 million a year because they educate half a million pupils at no cost to the state.
Jonathan Shephard, the council's general secretary, said: "Almost a third of pupils in ISC schools get help with fees. The tax benefits of charitable status are far outweighed by the amounts given back in fee assistance."
The bill does not specify how often the Charity Commission would need to check schools. However, it would grant the commission powers to enter premises, seize documents and order trustees to act if there were signs of administrative misconduct or mismanagement.