A consultation paper from the Charity Commission sets out the principles for being a charity - a status that can give private schools tax benefits.
Eventually private schools may have to show they offer bursaries or share their facilities with state schools.
The Independent Schools Council says most schools already run such schemes.
Most independent schools have charitable status, which until recently was automatic for non-profit schools.
But the Charities Act 2006 changed that and now all charities must show they provide a public benefit.
The consultation paper, published on Wednesday, is the first step towards detailing what schools must do to retain their charitable status.
The key principles are that there must be an identifiable benefit to at least one section of the public and that people on low incomes must be able to access the charity's services.
