The American management guru W Edwards Deming (1900 - 1993), credited as the brains behind Japan's industrial upsurge in the Fifties, would call up members of his lecture audiences and set them to work on little experiments.
Here's one you can try - your children will like it too, and there are obvious curriculum links - to science investigation for example.
You need a funnel, a moveable clamp to hold it, a marble small enough to go through the funnel, a table with a white cloth and a felt-tip pen.
With the pen you draw a target on the cloth. Then you drop the marble through the funnel a number of times. Your aim is to land as closely as possible to the centre of the target. On the first try, the marble probably misses the centre. So you mark where it lands and move the funnel to compensate.
But it doesn't work - in fact the more you persevere with moving the funnel to correct for the errors, the more your hits wander off. And, if it were one of his lectures, Deming, in the role of manager, would castigate you for your ineptitude ("Come on, do something! Move the funnel!") to the delight of your fellow audience members.
Deming's point is that the errors have nothing to do with you. The system just isn't good enough to deliver consistency.
What does this have to do with the task of leading our schools? Well, imagine observing a young teacher and concluding that some lessons are good, some are satisfactory and some are terrible. How often might we shake our heads and urge her to adjust her approach, like Deming ordering his subject to shift the funnel?
On reflection, however, we might conclude that factors that are our responsibility rather than hers - planning, mentoring, behaviour policy, subject leadership - are so loosely constructed that she's never going to hit the target reliably.
Sometimes she'll delight herself and think, "OK, then - so that's how it's done!"
But then she'll find that despite a huge effort to repeat the trick, the next lesson is inexplicably even worse than before. (Come on, you know that's a familiar story. Just read the TES "Staffroom" postings.) A key Deming message, then, beautifully illustrated by the funnel experiment, is that very many people work hard trying to achieve targets which are beyond their control.
"We are being ruined by best efforts," he said.
For details of Deming's management ideas see www.deming.org.uk