I think about him every day. Not obsessively - the days of “if only” and “what if” are behind us. But every day, some event triggers another thought. The thoughts are increasingly angry ones.

I work with excluded students. Truants. Aggressors. People involved in crime. We try to help them develop skills and gain qualifications which will enable them to get work. It’s difficult, but we usually get some sort of positive response.

Then there’s Des. No criminal record but on everybody’s “at risk” register. Des is excluded and has missed, one way or another, almost a year’s schooling. He is not pleased to be back in an educational establishment and is not ready to learn. He is confrontational and abusive.

Des was amused when we heard that a fellow student had been involved in a road accident. He described such people in most abusive terms. “I wonder what that makes my son?” I muttered to myself. He heard me and repeated his comment. Another student explained my circumstances. Des laughed and shouted: “Just f***ing proves it!” I had to go home. It was too much to be in the same building as Des.

Martin, on the other hand, has the same rough edges but a touch of humanity. We were discussing the role of parents. Martin said that mothers were there to nag. “My mum’s always going on about riding carefully when I’m on my bike. Shouts at me if I haven’t got my helmet on.”

“Sounds senible to me,” I replied. Martin sat silent for a moment before apologising, “Sorry. Your son. I forgot.” No offence was intended or taken. In this case, my son’s death became a positive - if distressing - talking point.

But sensitivity is becoming a rarity among our students. They boast about beating up all-comers on a Saturday night. They boast about taking illegal substances. They direct abuse with equal ferocity towards us and their parents.

I think about home and about bringing up my own children. Not without conflict, but always with a sense of trust and respect - and a great deal of affection.

In my 30 years working with kids, I have tried to treat each of them as though they were my own. To worry about them and care for them. To show a level of respect and encourage respect in return.

But I can no longer face this horde of self-confessed thugs, who care for no one and reject offers of help. Without doubt, some have had a series of bad experiences in school which will have turned them against teachers. Without doubt, some are intelligent and could gain qualifications and find jobs worthy of their intellect.

But it is hard for me to reconcile the fact that they, who claim to be unloved, are here - and our son, who was loved, is not. It is hard for me to find the enthusiasm to work with these kids and continue to turn the other cheek as they abuse us. But continue I must - for what else is there for them?

The writer, who wishes to remain anonymous, works at a pupil referral unit in East Anglia