Elspeth Insch is a firm believer in the support her school receives through its membership of the King Edward VI Foundation in Birmingham.
The foundation, set up by royal charter in 1552, has been cited by ministers as an example of the collaboration that schools could benefit from if they formed trusts.
Today it supports five voluntary-aided grammars and two independent selective secondaries in the city, all dating back to at least 1883.
The foundation owns their assets and buildings, appoints the majority of their individual governing bodies, employs their staff and provides shared central services. Heads and teachers from the seven schools also meet to swap ideas and expertise.
"It means you have got colleagues with similar issues and problems to hammer things out with," said Ms Insch, head of King Edward VI Handsworth, a girls' grammar.
"It really is a case of your greatest rivals are your greatest friends."
With around 6,000 pupils and 1,000 staff to serve, economies of scale allow the foundation to provide a high level of service.
It looks after the schools' finances, personnel, building projects, relations with central and local government, exams, governor support, and runs a graduate teacher-training programme with 25 trainees a year.
The foundation's annual pound;2 million income from its land and investments also means the two private schools can afford bursary schemes while their five state cousins receive an extra pound;200,000 a year each.
Steven Grainger, secretary to the foundation's governors, said it provided the schools with stability, support and allowed heads to focus on teaching and learning.
He cannot see the point of the Government's proposed trusts unless more than one school is involved.
Ms Insch said it was essential for schools considering a joint trust to have the backing of a team of high-quality specialist staff who could act like a "leaner and meaner" mini local authority.