He thought nothing more about it until the next day when he was summoned to see the headteacher who told him that the boy's mother had complained. The head checked the facts, saw the mother and tried to smooth it over. She brushed aside the attempt and made a formal complaint to the local authority.
My friend found himself facing an allegation of physical assault and a demand from the mother that he apologise to her child. The local authority, as it was obliged to, convened a preliminary hearing and witness statements were taken from the children and the other teacher who saw the incident. They all corroborated my friend's account. Nevertheless, it could have got very nasty if the boy's parents had not fallen out, and at the insistence of the father the complaint was withdrawn.
The boy, meanwhile, has been exploiting what he sees as his enhanced status. Soon afterwards he was strolling down a corridor with his tie defiantly at half-mast. Normally the headteacher, a stickler for such things, would have straightened it, but when he saw who it was he backed off. The boy smirked.
My friend survives, dismayed and at a loss as to what to do with unruly pupils. He is not alone. There are many similar stories of teachers in the parental firing line rather than getting their support. The lack of reinforcement may also extend to governors and local authorities. Manton Junior School in Worksop and The Ridings in Halifax are only the most recent examples where the official view has been that disruptive behaviour is "a challenge".
But how is the challenge to be met? The old-fashioned clip around the ear has long since become taboo. However, as my friend's case shows, almost any kind of physical contact leaves the teacher vulnerable.
For routine misbehaviour a child can be set to litter-collecting, or lose some privilege like being able to stay in the classroom at lunchtime. Or the parents may be called in. Teachers joke that the telephone has replaced the cane. But even in the leafy suburbs this sanction seems to be losing its effectiveness, because parents are more inclined to back the child.
Detention has also lost much of its force since there are now requirements to give at least 24 hours' notice and obtain parents' permission. Some refuse, saying it is unfair, or their son or daughter would miss the school bus. Trying to control routine misbehaviour is taking up an inordinate amount of the time of form teachers, pastoral tutors, deputies and heads.
Over and above the misbehavers, there is a hard core of persistent and extreme disrupters who appear to have almost no sense of right and wrong, and show little remorse when confronted with their wrongdoing. Most schools are severe only when it is plain that the pupils will not modify their behaviour or see the error of their ways. In these cases, the school can recommend a transfer, call in a psychologist or the police if relevant, suspend, or, as a last resort, expel. The new laws force schools to exclusion earlier than they would wish.
It is not easy to see how schools in the current climate can get a grip on the situation. Home-school contracts might help, but it is difficult to see how they could be given "teeth". Neither would they help in a case which I know where a mother admitted her son was out of control, but expected the school to solve her problems as well as its own.
Rewarddemerit schemes linked to the record of achievement could provide incentives for good behaviour and some deterrent to bad. "Time-out" rooms under sergeant-major types could bring a measure of control in some cases.
Greater use could be made of external referral, but those services are being cut back. Changing the law on suspensionexclusion, as the Secretary of State has promised, would mean that these could be more sensibly used. Sanctions will only work, however, if the teachers are backed by parents.
It is all very well for Esther Rantzen to go batting on about children's rights, and the Government about those of parents, but what about the authority of teachers and school discipline? Teachers are acting on our behalf to educate our children and help to make them civilised members of society. They must have at their disposal an acceptable and effective set of sanctions to apply to the unruly. This is important not only for the miscreants themselves, but for all those whose education is being disrupted by children out of control.
It is a truism, but nonetheless important, that educating children is a partnership between teachers and parents. If the behaviour of some children is getting out of hand it is at the door of both. Most parents recognise this, but an irresponsible minority are more than indifferent - they hold teachers to account to the extent that it amounts to actual abuse.
Alan Smithers is professor of policy research and director of the centre for educational and employment research at Brunel University.