We all have the capacity to be childish. We work with children, after all - and their responses do rub off. And however mature and professional we try to be, there is always a little bit of us that wants sweet revenge. We are only human.
This all started when "Josh" turned up to school on a motorbike for his science GCSE exam. It roared up to the school, making him sound so very important and shone in the sun as it swerved through the massed anxiety in the yard.
It was not, of course, the bike he had fallen off the previous week. He had been in casualty for quite a long time while they picked the gravel out of his leg. The bike was a write-off.
Apart from road-rash he was all right, and he had developed no aversion to motorbiking. Indeed, he had got a new bike after the accident. But we didn't know that. Neither did we know he was out on the road again, nor that he was planning to come to school on it. We hadn't approved that.
His head of year was furious. His first response was to wheel the bike away and hide it - an understandable, if unexpected, response.
Some might worry that this action could have upset Josh before an important exam. But while the girls huddled together doing last-minute formulae revision, he just leaned against the wall, bored. Josh has always been a pain.
We had taken Josh on from another school where he had been accused of stabbing another child with a pair of scissors. He hadn't, but the accusation was enough for them to move him on. They did not regard him as an asset.
Once at school, there had been a time when he was pursued by drug dealers for an unpaid account. It made for a rather exciting lunchtime. But generally he has been nothing much more than an irritant - a constant one.
His performance in exams has been similarly uninspired. He has been there for them - I'll give him that - but only because we threatened to invoice his mother if he missed them. His mind has been elsewhere.
He turns up and sits in the exams like a stone. He writes his name and then stares vacantly at the clock until his forehead sinks upon the desk.
We prod him and he writes a few random words.
But it is a waste of time. The only person who benefits is the examiner who is paid to mark his paper.
So the threat to hide his bike seemed a reasonable response to me. But my colleague decided to embellish it. He told Josh that it had been taken away by the police to be crushed. Some vague offence was invented.
Josh merely shrugged.
He didn't seem to care. He would get another one.
He will, too. His absent father will buy him another. And Josh will never take any responsibility for his actions - because his father will sort everything out for him.
We sigh and sanity is sadly restored. We give him his bike and watch him drive noisily away.
He has wasted his time - in school, in exams. He has wasted our time, and wasted our money. And when he leaves school he can concentrate on wasting his life.
Geoff Brookes, Deputy head, Cefn Hengoed School, Swansea.