It is the elephant in the room. It is the issue that successive governments have danced nervously around without ever addressing head on. I refer, of course, to the divide between independent and state schools - the greatest source of untapped potential in the entire education system.
Three weeks ago, in a speech that was heavily misquoted in the media, I said that a profound divide had grown up between the two sectors, and that both main political parties were responsible. The Conservatives don't dare ruffle their constituency of fee-paying parents, while state schooling is sacrosanct for Labour.
Six years ago, I wrote pamphlets for the Institute for Public Policy Research and the Social Market Foundation on partnership between the two sectors. Since then, links have increased, involving small as well as larger independent schools. But funding has remained minimal, just some pound;15 million over 10 years - pathetic when one considers the opportunities to be gained and the constant calls for extra funding. Lip service has been paid, but it is not yet a serious plank of government policy.
When I called for a new vision recently, I was attacked from both left and right, often, regrettably, with incorrect data. The hostility that emerged was striking, and it successfully diverted attention from my argument. So I return to the subject today.
Let me state the proposition very clearly. State and independent schools are having far too little meaningful contact: the schools themselves, pupils and teachers, as well as the sectors, would have so much to gain if the contact was more significant. If the 21st century is to differ from the 20th, we need to take this subject seriously.
The traditional tack of independent schools, even before the Charity Commission began its slow rumble, has been to give bursaries and loan out their facilities. They also ask, quite reasonably, why they should feel compelled to do anything, given that many have no fat to burn and their parents are already effectively paying twice for school fees. Bursaries and facility loans are both worthy responses, but neither is the complete answer. Scholarships for children from less well-off backgrounds take the most able away from the state sector and leave a lingering sense that it somehow isn't quite good enough to cater for the most talented. Offering facilities is good, but buildings are no substitute for human interchanges.
The independent sector is a jewel in the crown of British education. Its schools are rated among the very best in the world, achieving exceptional standards with often quite unexceptional children at A-level and GCSE, as well as in the arts, sports and all other spheres. Its pastoral care, based on vertical house systems, is copied the world over and, when run alongside horizontal year systems, it gives a "tartan" coverage that is far more inclusive than relying on a heads-of-year system alone. State schools also have much to teach independent schools, not least about monitoring pupil performance, professional development of staff and outstanding teaching.
What might an enlightened partnership system look like? At a sector level, independent heads could all affiliate to the Specialist Schools and Academies Trust and regularly meet their counterparts: this would open their eyes to much that is going on in education. The National College for School Leadership could also galvanise cross-fertilisation. Independent schools could start academies or join in federations and trusts with state schools.
At a school level, teachers, including heads, could meet and take part in exchanges. Pupils, too, could exchange and work together on joint projects. At present, sports fixtures are the most common way in which children from the two sectors interact - hardly an ideal starting point for mutual understanding and respect.
The dwindling band of naysayers is locked into 20th-century thinking: they are selling their schools and pupils short.
Anthony Seldon, Master of Wellington College in Crowthorne, Berkshire.