Yet it is one that has been neglected and ignored for far too long by the education establishment - and, dare one say it, the education press, which peddles debates of minor importance to those who are actually in the business of teaching in and running schools.
My columns have regularly highlighted that the prime education question for Britain today, the one that should be at the pinnacle of the agenda, is:
"What on earth is the purpose of education, and why are we not making a better job of defining it, and then designing schools to meet those objectives?"
In this slot last last month, Peter Wilby discussed a pamphlet to be published later this month by John White, the distinguished emeritus professor of philosophy of education at London university's Institute of Education, What are Schools for and Why? Like all genuinely important tracts, it is brief, straightforward and intelligible, and should be read by all involved in education.
Professor White asks absolutely the right questions, but falls short in his answers. Too orthodox and establishment. The curriculum in schools today resembles a dilapidated house on the outskirts of Mumbai. Over the years, its owners have slapped bits on to what was once a coherent building but is now a mishmash of styles, materials and hazards. Today's curriculum has been shaped primarily by universities, employers and successive governments, yet none is entirely happy with this house. Children's extra-curricular life is more the product of individual schools, but the quality and range of these activities have been shamefully eroded - in state schools at least - over the past 15 years. Would that a flood might come and sweep away the whole rotten building.
The core question is: what should children by the age of 16 or 18 be able to understand and know? And who should they be? And what should they be able to do? Answers to the first two questions involve a knowledge of society, language, maths and science. We can debate the niceties of these, but most would broadly agree. The answers to the two latter questions are core and lie in one's view of what it means to be a human being.
Our model at Wellington holds that all humans have seven faculties: left-brain and right-brain ability and sporting, artistic, social, personal and spiritualmoral aptitudes. The job of all schools is to identify, nurture and enhance those faculties, in the knowledge that what is not developed at school is unlikely to be developed later.
Some, including Professor White, have philosophical problems with this approach and say you cannot design a school around such abstract notions of the "human". I say forget the philosophy and go for common sense. Schooling for many children barely begins to rise to the challenge of developing all their faculties, thus denying them the chance to live full and valuable adult lives. This is tragic because it is avoidable.
May Professor White's pamphlet begin a national debate.
Anthony Seldon is master of Wellington College in Berkshire