ONE LINE from the pitiful trial of teacher Peter Harvey, who battered a disruptive pupil with a metal dumbbell, stands out above all the others.

In court, a classmate of the victim admitted pupils would secretly film teachers as others tried to “wind them up”.

The footage was then shown around the school because it was “funny”.

In this sentence you can see the stark and horrible reality of too many classrooms.

Children who have become vile and disruptive. Teachers who have been ground down through lack of support. Rules being broken as routine.

And a society which seems to regard tormenting someone to a breakdown and placing footage of their distress on YouTube as entertainment.

I’ve seen clips taken a few years back at my own kid’s school, of a child running around on desktops while the adult present in the room appears to ignore what’s occurring.

I’ve seen footage of other pupils trying to shove a set of metal lockers downstairs, while being cheered on by classmates.

This isn’t a broken, inner city school. It’s a rural establishment in a posh postcode where kids are regularly ferried to school by parents with his ’n’ hers Mercedes.

I mention it to show that the problem of so-called “low-level” disruption, the kind of behaviour which leads to high-level disruption, is endemic.

And the reason it’s endemic is because no government or local authority has the guts to tackle the issue of behaviour in schools, whether it’s putting up with weak, ineffectual or bullying management, or giving the correct support to the strong managers who identify the trouble-making kids and want to boot them out.

The majority of teachers are competent and know their stuff. The majority of kids are well behaved, or would be if they knew what would happen to them if they weren’t.

But the old certainties have been eroded by the culture – cancer, even – of inclusion, where teachers must pander to violent or badly behaved pupils and where the only sanction is a few days’ exclusion.

Imagine if your kid was in Harvey’s class and actually trying to learn something?

Remember, this school is one where the head teacher is pleased to inform parents that: “We insist on high standards of behaviour and self-discipline to help students achieve and to prepare them for life after school.”

Really?

No wonder that so many of those who can, strive and strain and beggar themselves to go private or buy homes next to the outstanding schools.

Only this week we saw the former education secretary Ruth Kelly snap up a £1 million house within sneezing distance of what is arguably London’s best state school.

How lucky for her, funded, as she has been, by our taxes. How unlucky for all those children for whom such life-enhancing education is still just a dream.

“Mr Harvey just went mad,” one pupil told the court hearing. He’s not the only one. We’re all mad to put up with it.