Independent schools could "lend" teachers to state schools in their local area as a way of justifying their charitable status, new guidance says.
It suggests shortage specialist teachers, such as those in modern languages or separate sciences, could be seconded for extended periods.
Fee-charging schools, which benefit from pound;100 million in tax breaks for charitable status, could also open their doors to state school pupils to attend certain lessons, the Charity Commission said.
New draft guidance was released for consultation this week, a year ahead of the deadline for fee-charging schools to report on the benefit they provide to the public.
Schools found not to provide a benefit face losing charitable status and tax breaks. The commission says independents could work with state schools to boost their success at university entrance. It suggests they raise fees to pay for bursaries and scholarships for those who cannot afford to attend the schools.
Schools' arts and sports facilities could be opened to the community. The guidance also suggests an exchange of expertise, with state and private sectors helping each other to make improvements. An example suggests an independent school could help a state school set up a sixth form, and state schools could help an independent to "develop its approach to arts and drama".
Schools could hold joint events and work on research-based projects to "improve teaching and learning in the local area". The guidance also advocates independent schools sponsoring academies. So far, 20 are sponsoring or planning to sponsor academies.
As the guidance was released, Winchester College announced it is planning to sponsor the new Midhurst academy, 30 miles away. Ralph Townsend, the head, said: "This is a wonderful opportunity for Winchester to look outward, to share our knowledge and experience with those with similar aspirations and learn from our partner organisation."
Dame Suzi Leather, chairman of the Charity Commission, said: "Although some debate has focused on independent schools, this new draft guidance is intended to help all charities that charge fees, whatever the focus of their work."
The Independent Schools Council has threatened taking legal action over the draft guidance. Jonathan Shephard, chief executive, said: "The guidance has drifted so far from the law that it comes close to ignoring, or even attempting to reverse, some fundamental legal authorities. The role of the Charity Commission is to apply the law, not create it."