At any performance, breaths are indrawn and giggles explode at moments which betray the presence of teachers, ex-teachers, governors, sixth-formers, and possibly the occasional inspector.

Laymen’s laughs are different in quality: anyone can enjoy “History, it’s just one f--ing thing after another” or Frances de la Tour’s magisterial lament, as Mrs Lintott, at having had to teach “500 years of male ineptitude”. The really interesting laughs, and gasps, are at lines which hit home when you are actually close to a school.

There is the headmaster’s testy complaint that the old, liberal teacher Hector gets results with the boys all right “but nothing I can quantify.”

There is the riposte from the old reprobate that “the main enemy of culture in any school is the headmaster”.

But the one which struck me most forcibly, and stays with me, is a line at the very end, spoken by the ghost of the maverick, long-serving and inevitably disgraced Hector. “Pass it on,” he says with weary, dogged conviction. “Pass the parcel.”

It is about transmission of culture, transmission of knowledge, perception, canonical art and centuries of human thought. And it seemed to me to speak directly for Bennett himself, who rarely draws conclusions in any of his work but merely rolls up what he has perceived and understood and discovered, and passes it on - in the hope that someone else, some day, will find it useful. Maybe, he implies in that diffident Bennett manner, they will make better use of it than he has.

I suppose that is what a traditional teacher does. Don’t bother over much with “learnacy” or get hung up with teaching theory: just tell the story, convey the truths and the experience of the centuries. Roll it all up, give it handles the young can grip, pass it on. A headmistress - rather an old-fashioned one - said to me once that no teacher should ever retire until he or she was sure that a good number of former pupils were themselves teaching, so that the line of transmission was assured. I asked whether parents counted, and she hesitated.

“No,” she said. “Parents are delightful amateurs. They only tend to pass on things which they are themselves deeply interested in. A teacher passes on everything, even things which don’t touch her very deeply, because they might be useful to someone else.”

Her example was of her own history teacher, a fiery man whose account of the French Revolution had led her towards a PhD and a lifelong fascination with the subject.

Years later she met that teacher at a party and told him what she had done with her academic life. He roared with laughter and admitted to her that the bloody French Revolution bored him to tears, and he always dreaded teaching it. She talked to him for half an hour, at the end of which he conceded that mmph, yes, she had found more in it than he ever did, and he was grateful to know that. Might even read the books again himself, now he was retired.

I was thinking about this as the term ends. Inevitably, most schools see long-serving teachers retiring. Heads, always keen for the new blood, modest salaries and theoretically higher energy levels of young teachers, tend to express civil and grateful regret at such moments while feeling a surge of inward relief. This is only natural.

There certainly are some lifers, long-serving teachers, who are worn out, bored, jaded, disillusioned, grumbling, idle and a thorough pain in the neck.

But there are others, in all subjects, who are precious: who like a smooth spade-handle shine the brighter and silkier from long years of polishing and perspiring. They never lose the longing to roll the knowledge up, give it handles, pass it on. They never lose the hope that a pupil will outshine them, understand better, take the knowledge further. In class, less anxious than their younger peers, they never miss a chance to divert profitably from the aridities of a set curriculum, and surreptitiously point the interested in other interesting directions. In a good school, they also hold the ethos and unique soul of the place in their hands, and pass on the best of it down the ranks.

Mr Chipses and Ms Chipses, never tend to make it to headships (that aspect of the story today seems a piece of wild fiction). But they do something which may be more important, with self-effacing faithfulness and clear, lifelong purpose. If someone in your school retired this summer, full of years, and leaves a gap behind, then raise a glass to him or her. Ripeness is all.