This month Birkenhead High School, a high-achieving independent girl's school in the Wirral, surprised many with the announcement that it was to join the state sector as an academy. Why is a successful, popular school, crossing the floor? The answer is simple: public benefit.
Since the Charities Act came into force last year, schools are having to prove their public benefit or face extinction. Some heads see it as an irksome distraction, and a sudden rash of new projects can look cynical.
Among the cynics and doubters are many sincere believers. The Girls' Day School Trust (GDST), a charity that runs 29 independent schools in the UK, reckons public benefit benefits students, too. Birkenhead is the second GDST school to join the academies programme. The Belvedere School in Liverpool was the first independent school to turn into an academy, admitting its first fully state-funded cohort last month.
"GDST's roots are very much in responding to inequality," says Barbara Harrison, chief executive at the GDST. That has traditionally meant the broadest possible access. Until the late 1970s this was achieved at Birkenhead under direct grant schemes, then by assisted places.
Since the late Nineties the GDST, like other schools, has had to fund its own bursaries. Birkenhead and Belvedere chose to work with the new initiative rather than restrict access. "We couldn't fund the number of students who wanted to be there," says Harrison. "You can't achieve anything of that scale without government support."
Five independent schools have announced that they will become academies. Harrison says some independent schools have applied and been rejected. Schools looking to make the transition, says Harrison, need to be high performers in poor areas, where state provision is weak.
Broadening access does not mean opening the doors only to fellow Brits. For the past three years the GDST has run an international summer school with HSBC at Nottingham University. Next year the first GDST franchise school will open in Shanghai.
"We felt we should bring an international dimension to our schools, to develop our students as citizens and promote greater cultural understanding," says Sue Bridgett, the trust's director of communications and development.
The Shanghai school is to be linked with Oxford High School. With site and buildings paid for by local investors, this approach is less expensive, if harder work, than bursaries. The trust even expects to make money, to reinvest in schools in China and in the UK.
Partnerships are the core of public benefit. Many independent schools work with the local community, and the Charity Commission recognises this as one of the best ways schools can act in the public benefit.
This can mean sharing resources. Several GDST schools help maintained schools teach languages, while Blackheath High School offers after- school and Saturday classes.
Or it can mean getting the children to work together. Wimbledon High School is involved through London Challenge Partnerships with a local comprehensive, offering Easter revision courses, and organising master classes for the gifted, and a conference on crime, or the Olympics.
"It's not one-way traffic," says Pamela Wilkes, head at Wimbledon. "Sharing ideas with children from different backgrounds gives students a different perspective."
Some partnerships throw up more tangible benefits for students from the independent school. Since 2005, Sheffield High School has worked with local schools as part of an Aim Higher project to demystify Oxbridge entrance with meetings, visits, interview practice and advice.
"It has made a terrific difference," says Valerie Dunsford, head at Sheffield High School. Applications and success rates at local maintained schools are up. And at Sheffield High School the number of pupils offered places at Oxbridge has nearly doubled.
"They see that it's not something they're going through alone," says Dunsford. "When they see 200 or 250 students doing this, they don't feel in a minority." Independent school pupils are part of the public too.