John tries his best. I know that. He doesn’t really want to be naughty.

It’s just that he doesn’t always know what to do. Sometimes this gets him into scrapes in school. He’s always sorry afterwards, and always knows he has made a mistake. But he can’t seem to stop himself saying or doing the wrong thing.

His whole life is a struggle - a battle against his circumstances. For, even at 12, he knows his way of life cannot be sustained.

When his parents arrive at school to discuss his latest difficulty, we are reminded why. They are dirty and toothless. They are mocked mercilessly by the local community because of their slowness and inadequacy. They are in their early thirties but look like 50-year-old crones. They drag through the door with them John’s younger brothers and sisters, who crawl all over the room, spilling the contents of their overfilled nappies on the floor.

The children dismantle the telephone. They scream and shout all through the interview. This is part of the deal. If you want to speak to his parents, this is what happens. And this is what John has to face when he goes home at the end of every day.

And you stop and think when you see all this, and you begin to realise that no matter how often he is in trouble, what John does manage to achieve is remarkable, for his home life has no shape, certainty or pattern.

John’s parents are clearly out of their depth. They love their son and want him to do well. He is not beaten or disciplined. But he is abused because he experiences low standards of care from parents who themselves have special needs. John is malnourished, of that there can be no doubt. Sunday dinner is pizza and chips. His teeth are yellow, his pockets full of sweets.

He craves attention in a desperate kind of way, and at times becomes almost catatonic, refusing to speak and curling himself into a ball, trying, it seems, to cut himself off from the world. Social workers are involved with the family, but they can do little to change its direction and shape.

This is the biggest influence on his life. He does want to get out of these circumstances. He knows that what is happening to him isn’t right or normal.

He thrives on attention and loves being read to; he will sit listening to me in class for hours. But, like a magpie, he is attracted by shiny pencils and new things. This is stuff he likes but knows he can’t have. So it always seems to find a way into his pocket. This makes him unpopular with his class.

He can be awkward. He can be disruptive. His writing is messy, largely unstructured, representing an outpouring of ideas from a frustrated mind.

His whole problem for me is that he has no one on whom he can model himself. He needs a template, but there isn’t one at home. He is like a boy lost in Derby trying to find his way with a street map of Bristol. His experience has no shape, no pattern, no boundaries.

Of course, he is not alone. There are children everywhere who are trapped by the past that made them. They face a future for which they are not suited. They never find a motivation to achieve, internal or external, because they have been cheated by their circumstances.

Progress. Achievement. These are alien concepts. It is home that shapes them. School can offer much - sometimes an escape, a route away. But not always. School cannot be expected to change the home.

Look at Lorraine. She is, in school at least, a quiet creature. But she is wilful and difficult and often refuses to come. Her parents have therefore implemented an incentive programme. I suppose you can say it has worked in its own way, but now she will come to school only if her mother continues to give her cigarettes. So she does. Lorraine is 11.

Christine had the brightest, most incisive mind I have encountered in 30 years of teaching. She should have gone on to university. She had the potential to become a significant someone. But her home was shocking. Her parents were unable either to recognise this or to do anything about it.

And from the chaos of her home she has been reduced to selling the evening paper on street corners, her potential stifled.

Of course, some children escape from inadequate homes. But many do not. The lost boys. The lost girls. These are not isolated cases. All teachers can tell these stories. In our schools, we can see their faces, their futures fixed. It is their destiny to form the underclass. I know this and I am powerless to stop it.

Geoff Brookes is deputy head of Cefn Hengoed school, Swansea. All names have been changed