Question: How do you turn a school around? Answer: Appoint a new head. The conventional wisdom of school improvement is that the simplest way to make a school better is to change the person at the helm. He (it is usually a man) is seen as the one thinking human being wrestling with brute machinery to change the course of the unresponsive hulk in his command.

The head, they say, is crucial. Research bears it out, here and in the United States. But not, interestingly, in Holland, where the personality of the ship’s captain isn’t quite so dominant a factor. That at least should make us ask more about the relationship between the teachers and their head, rather than focusing solely on the figurehead. It’s dramatic, lazy and cheap to think that changing one person is all you need to do to change a school. It’s nothing like enough, and in any case, the supply of candidates is running out.

Where do heads come from? They’re deputy heads who have been trained, have emerged through a tough selection process, and - any minute now, at an academy near you - will have been stamped with the NPQH, the new headship qualification. So that’s all right.

Except that there aren’t as many deputy heads as there used to be. In my authority I know of four schools that have “lost” such posts in the last year. I know of none which has created new deputy’s jobs. It may be a response to a budget crisis, but it could also be a creative move, changing the nature of the hierarchy, spreading responsibility down the pyramid. If that is a trend, where are the new heads coming from?

Middle managers may well be gaining from the demise of the deputy, but it is unlikely that they feel directly equipped for headship as a result. So, overall, the pool from which heads can be drawn is shrinking. And within that pool, not all will become heads. Some fail to get headships, some lose heart, and others make a positive choice not to seek headship.

But there is another danger to the one-man-is-everything philosophy. There is no doubt that the pressures of management increasingly pull heads away from the educational business of their schools. Many heads are aware of this, comment on it, even fight it. But if New Labour’s strategy is to stick good heads into bad schools, then they’re going to have to find ways of helping those heads with the business of headship - focusing on learning, supporting and inspiring teachers, valuing work in the classroom. They won’t do that best if they’re inspired by images of splendid isolation.

The solitary captain is dangerous because it means hasty, unbalanced decisions, sometimes made in ignorance, and frustrated talent down below. It also places excessive strain on the captain. Finally, it creates problems of continuity: if headship is so different, so special, how do deputies ever get to learn it? The rhetoric of team management has been around for more than 10 years, but the practice is still rare.

If nothing changes, we may run out of headteachers. Heads will continue to retire early, and increasing numbers of deputies will look at the pressures of the job and decide to say: “So far, and no further. I want to hang on to my hobbies, spend time with the kids, go out now and again. So, thanks but no thanks”.

And that’s the short term. But this isn’t just about deputies, it’s about management in schools. And the long-term prospect is frightening.

Pick a school. Pick the best five teachers in that school, any subject, any age, and ask them: “Do you want to be a head?” My guess is that most will say no. Twenty years ago, maybe 10 years ago, most might have said yes. But now they’ve looked at what’s involved, the kind of lifestyle, contacts, pressures and choices that are involved, and decided it isn’t for them.

They may like their heads, or respect them, or feel sorry for them, or be grateful that their head enables them to do good work. But they see the job as different, more widely separated from their own than it used to be, and to many imaginative, creative teachers there is no strong reason for jumping across the gulf.

There is for some, of course. People who like to be on top, in charge, have always gone for headships, and some of them make good heads. But my worry is that increasingly this is the type of person who will wish to be a head.

The ones who want to do things differently, maybe to change the pattern, will get little encouragement and see many obstacles in their way - of which NPQH is only the first. So we may end up with a lot of ships being turned round by people who are there not because they have a particular course in mind, but because they like the feel of the tiller in their hands.

What am I asking for? Not anarchy, not less accountability, and certainly not for anything less professional in the process of preparing for headship. But I would like to see a more careful look at the way heads and their schools interact, an approach that placed less emphasis on the captain and allowed for a closer, more sensitive appreciation of the importance of the crew.

* Paul Francis is a deputy head in Shropshire.