It is only human to want easy answers to intractable problems and inevitably I started to wonder whether, had the north London headteacher’s young assailant been made to sit in a room like this and to hear such men’s stories of guilt and remorse and frustration and boredom, he might have thought twice before wielding a knife.

It is unlikely, of course. As those lifers would have been the first to point out, in the heat of fury or hatred or fear, thought just does not come into it.

Violence boils up from such a poisonous cocktail of different sources, there can never be simple answers. Exposing young delinquents to prison inmates (something the prison service already does) will have no more effect on rising violence than tightening up the *law on carrying a knife, or implementing any other single-issue measure.

The tide will not turn and, meanwhile, schools will have no choice but to carry on fortifying their defences, inch by pragmatic inch - locking doors, installing security cameras, shopping for hi-tech entry systems.

I feel sure of this after spending years in the United States where - as we have been told until we are sick of it - inner-city schools are fortresses of security guards and metal detectors and classrooms are kept locked during lessons.

What is not properly explained is that, far from being shocking manifestations of a society under siege, these things are as mundane and unremarkable a part of school life as history tests and basketball games.

This realisation dawns slowly. It is a genuinely shocking experience the first time you visit a besieged school and check-in with a guard, pass through a metal detector, pin on your security tag and watch students being sent to mind your car for the length of your stay. As you are shown around by a key-toting principal who unlocks each door as you come to it, you feel about as far from normal school life as it is possible to get.

But on the second visit it does not seem quite so strange, by the fifth you hardly notice and by the tenth you have come to understand - just as the students do - that these precautions are the very least any responsible school should be taking to try to keep pupils safe.

The truly insidious thing is not the guards and the keys, but the inevitable degradation of teaching and learning in such an environment. Everything is conducted in an atmosphere of constraint and tension - whether it is the principal who turns down an offer of work experience places at a local factory because it is “on a pretty bad block down there” and she fears the 10-minute walk will expose her students to unacceptable risks, or the teacher who no longer dares to put a caring hand on a student’s shoulder because “the kids are so wired now, if anyone touches them their first instinct is to hit out”. It is so pervasive that no one really notices any more. With weary resignation they accept it is just how things are.

“Ah”, we smugly like to think, “but that is over there. It will never get like that here.” Yet once upon a time, not so long ago, it was not like that over there, either - and things over here are already much more like that than we care to think.

All the preconditions of escalating violence are in place - the drugs and weapons, the marginalised teenage boys and disaffected young girls, the broken homes and poor housing, the bleak streets and bad diet. The only remaining differences are the lack of readily available guns - which keeps our death and injury rates at a more palatable level than in America - and the fact that we are a small, crowded island where communities cannot divide themselves off from each other as effectively as across the Atlantic. So instead of the USA’s stark black and white patchwork (metaphorically), we live in a diluted grey miasma of a society. Nowhere is as unutterably awful as the US ghettos, but nowhere is free from the relentless creep of anti-social behaviour.

In the small market town where we live, deep in rural England, every school has been broken into over the past year. There have been two child-snatching incidences, a drug swoop, and acts of drunken vandalism almost every Saturday night. One in three children at the local primary school now comes from a broken home, and the swearing and sexual aggression among even some of the youngest children is astonishing.

No one seems to find any of this strange except us, and we only find it so because we lived until recently in a leafy American suburb straight out of the 1950s - where an act of violence was a mail box sprayed with shaving foam at Halloween, a crime wave amounted to a child’s bike pinched from an unfenced lawn, and the sense of community was so thick you could cut it with a knife.

Yet people constantly suggest we must be happy to be home again, away from the alienation and violence of the USA - quite oblivious, it seems, to the scummy tide rising up around their own feet.

Yes, the USA is a violent and uncomfortable society. But so, increasingly, is Britain - and with crime up tenfold in the past 40 years and violent incidents in schools up by a third in the past 12 months, it looks bound to get worse.

Like it or not, schools will have to address the problems coming their way. If they are smart, they will at least save time and money by not re-inventing the wheel.

America may not have found any solution to school violence, but it has spent decades developing strategies to deflect and contain that violence. Using anger management courses, building design solutions, teacher hotlines, peer counselling, assertive discipline schemes and gang liaison officers, US schools are grappling with the problems of how to function in a violent society.

Sticking our superior British noses in the air and shaking our heads regretfully over “their” guns and “their” metal detectors simply will not do any more. American educators have information we badly need. We should make the effort to seek it out, assess it with an open mind - anglicise it, if need be - and see if it can be put to any use over here.