The silly season is nearly over. The term is moving to a close and further cohorts of students have left us for ever. For most of us, Year 11 leave in a banal and messy orgy of shirt signing, flour and water bombs, shaving foam and ritual burning of school uniforms. At least the upper sixth at a Cheddar high school tried to be original. As a parting gesture, five members apparently decided to mark the end of their school days by leaving a sheep outside the staffroom. Other sixth-formers glued garden gnomes to structures at the school.

The press loved it. Making great play of how careful the boys had been to leave grass and water for the sheep, the whole thrust of the reporting has been to portray the head as a miserable old spoilsport. The head’s eminently sensible response, it seems to me, was to insist that the boys paid their own exam fees. The school’s PTA has since chimed in, describing the incidents as “harmless pranks” and accusing the head of “over-reacting” Not surprisingly, the head in question has refused to comment. Rightly so. He is on a hiding to nothing. Just how did the students get the sheep into the school in the first place? By, it would appear, deliberately leaving a firedoor wedged open at the end of the school day and returning later that night.

If the head had let such a grossly irresponsible act pass unpunished, next year’s stunt would have been even more outrageous. On reflection, the boys probably realised they got off somewhat lightly.

And then, you may recall, there was Emma (not her real name). Emma is a bit of a card. Not content with a pierced lower lip, she decided shortly before her exams to dye her hair bright red. The school, conscious that every other pupil in the school might feel free to do the same, reasonably asked her to return her hair to its normal colour. Not surprisingly, given her pattern of behaviour, she rejected that proposal out of hand. The hapless headteacher was then forced to face a barrage of questions from James Naughtie on the Today programme.

Emma, bright girl that she is, had thought of another wheeze and turned up for her exams wearing a Beatles wig. In the end, no doubt, she achieved her aim of embarrassing her school and attracting attention to herself .

The reality about such japes is that invariably they place teachers - and especially heads - under fearsome pressure. All my colleagues dread this time of year. It is one of the worst aspects of the job and yet it is never discussed, as if we are ashamed to admit it happens to us. We all try ingenious schemes to outwit the perpetrators. One colleague always takes her entire Year 11 to Alton Towers for the day - a bribe which I am told is highly successful. The usual defence - that it is an end-of-school “tradition” - is difficult to break.

I have two solutions. First, to make it clear that such behaviour will always lead to serious consequences. (Insisting culprits sit their exams in isolation from other students, or even at home with an invigilator, is my personal favourite.) The second idea is more imaginative. I can recall the story of the disappearing biology department skeleton. For some days it looked like a boring old case of theft. Until sports day, that is. As one of the budding long-jump stars came speeding down the runway, he was suddenly confronted by Frankenstein (the biology department skeleton) emerging from underneath the sand. He’d been there for a while, attached to the strong but invisible thread which, when tugged from a distance, brought him suddenly to the light of day. The best thing about the jape is that I am not sure it ever actually occurred. The story has grown in the telling.

Emma’s wig and the Cheddar sheep will also become the stuff of legends. Funny they may have been, they would have been just as funny if the stories were made up. The fun is in the telling. I see no harm in letting the imagination run riot.

Dennis Richards is head of St Aidan’s C of E High School, Harrogate.