It started because Ashley cannot deal with buses. He is always in trouble, and there are younger pupils who provide him with an audience. This time he stuck large pieces of paper in the window of the bus for pedestrians to see. "Please help us. Bomb on bus."
An insensitive act in the aftermath of the London bombings, and he was reported to me by the bus driver. He stood there, all bored and adolescent, saying nothing. His slouching body was eloquent enough: "What's wrong? Can't you take a joke?" And, as they say, I lost it.
This was suddenly different, personal. Ashley stood there, blinking and confused in the face of my fury. My colleagues were not especially inclined to intervene. Because what Ashley did not know was that my daughter is a theatre nurse in London. She had spent a day in the operating theatre, part of the team trying to put victims back together following the terrorist bombings. She had seen things no one you love should ever see.
Ashley had unwittingly gone too far. His was not an offence against school discipline, it was an oafish response to something horrible. And it hurt me. Perhaps he was unable to understand the events in any other way, or frightened of the emotions the bombings stirred in him. But this was not the moment for counselling.
I bawled straight into his face, invading his personal space. He had to confront real feeling, expressed by a real person. A father, not merely a teacher. We cannot always act the part. There is a person behind the professional veil. And this time the veil was well and truly ripped.
The children see us getting angry about trivia all the time. It is a part of a teacher's day. And it is largely an act. I mean, what sort of adult can whip themselves into a frenzy of genuine anger over uniform issues? Mr Smith going ballistic over a muttered insult is part of the mythology of the school. A story passed on through each generation of students. But generally we stay in control.
This time I could not do it. I do not regret my rage. He deserved it. Later I felt sorry for him because he could never have predicted the consequences of what he did. I am not sure he knows why it happened. Possibly it was counter-productive. All he has learnt is that sometimes it is wrong to upset Mr Roe. But I am afraid to say that I do not much care.
Ian Roe is a secondary teacher in north Wales. Names have been changed to protect confidentiality