The problem is "spoilt little princes and princesses," who are influenced by a "materialistic society" and a "culture of immediacy", says the National Association of Schoolmasters, Union Of Women Teachers (NASUWT).

The problem is "incidents increasingly concentrated in a handful of schools serving disadvantaged areas," suggests the National Union of Teachers (NUT). The problem is pupils with "deep-seated problems" who are being "failed by social workers," argues the Association of Teachers and Lecturers (ATL). The main teaching unions, at their Easter conferences, may have expressed their worries in slightly different ways.

But all are concerned about pupil behaviour, some of it low-level but disruptive to the rest of the class, and a small, but increasing proportion of it extremely serious, involving drugs, knives or guns. All the unions are concerned, too, at the lack of back-up that teachers often receive when they contact the parents of a misbehaving pupil. As well they should be. Without support at home, there is very little that teachers can do to curb poor classroom behaviour. Sometimes the parents sound no more mature than the children. One teacher called the mother of a boy who had applied shaving foam to his face in class, for the amusement of his fellow pupils. The teacher was told in no uncertain terms that the child could not possibly be held accountable because the boy who had brought the foam into school was the real culprit. The call took place within earshot of the child who had caused the trouble.

Download the new Independent Premium app Sharing the full story, not just the headlines

Another, who threatened a girl who would not stop talking in class with a call to her mother was told: "Call her then. She's slapped three teachers already." The teacher then spoke to the mother, and listened with feigned sympathy as she related the trio of incidents that had ended in violence. By the end of the conversation, the mother agreed that none of this was helping her daughter, and that she, too, did not know what to do with her, because she couldn't prevail upon the teenager to obey instructions either.

The teachers who describe such incidents emphasise that these pupils do not come from materially underprivileged backgrounds. Echoing the observations made at this week's NASUWT conference, about little princes and princesses, they say that family hostility to education often comes from households who have achieved some affluence without being well-educated themselves. They have their own tales of woe, about how their teachers told them that they would never amount to anything, and how their success has proved their former tormentors wrong. They distrust and despise teachers themselves, and see them as losers and mugs. These families have jettisoned the idea of education as a route out of poverty, and their influences can be seen in the anti-learning attitudes that are common among many school children, and can seem almost contagious even in primary schools.

One listens to these tales of frustration in the classroom with a sinking heart. What could possibly motivate professional people to put up with such behaviour, from children and from adults? A large proportion of teachers continue to train, teach for a time, and then give up the profession. It is easy to see why. Attempting to teach people when their entire families are hostile to education must be a nightmare. But when the NUT calls for "more support from parents on discipline", it is hard to work out exactly how this can really be achieved, given the prejudices of the parents most likely to send their children to school with poor attitudes.

Some of the methods suggested by the unions in the last week have been disturbing. The ATL, traditionally the most moderate of the teaching unions, has agreed that all children who have reached the age of criminal responsibility – which in England and Wales is, grotesquely, just 10 – must be prosecuted if they assault a teacher. While it is easy to understand that this demand is born of frustration, it is still deeply worrying that schools should be so willing to provide a conduit into the criminal justice system. A pupil who assaults a teacher, almost by definition, is one who has "deep-rooted problems". The criminal justice system has a far from unblemished record on either dealing with these problems or with setting children back on the educational straight and narrow.

There is no alternative for pupils this troublesome, at the moment, except pupil referral units. Yet the NUT, the biggest and most powerful teaching union, has at this year's conference made explicit once again its opposition to "sin-bin" schools.

Do schools specialising in children with behavioural problems have to be "sin-bins", as so many presently are? Or could they not simply be schools that embrace firmly the measures the NUT is lobbying for at all schools: small class sizes; more freedom from the curriculum; and more support from parents on discipline (with staff on site whose job it is to work with problem families)? Is it really fair to make inclusion in the mainstream such a priority that teachers and co-operative pupils have to struggle on until transgressions are of criminal proportions?

The difficulty here is that the vast majority of parents and the vast majority of teachers want smaller class sizes for all pupils. Sin-bin schools are seen by educationalists, rightly, as a bad idea. But rewarding families for their lack of commitment to education with privileges that almost everyone wants is seen as being vastly problematic too (although the Government has gone some of the way down this path with its proposals for small "studio schools"). Class size is so high on the agenda of teachers at the moment that the NUT has threatened to strike if the Government does not renew its early commitment to driving class sizes down. Both research and common sense attest that even a small reduction in class size has a positive effect on discipline and behaviour, even though it also seems incontrovertible that dramatic reductions in class sizes need to be achieved before real academic advantage is gained (research shows that there is not big step-change in pupil achievement until classes are of 15 or smaller, as they usually are in independent schools).

The infrastructural problems involved in attaining such a target overnight are phenomenal, and the cost, as the Government clearly discovered early on, is prohibitive. Yet it must surely be possible for reductions in class sizes to be achieved gradually, from the bottom up, with the schools experiencing the most severe behavioural difficulties – and presumably therefore the ones most likely to be undersubscribed – being given priority.

Many schools are de facto sin-bins anyway, not only because they are in deprived areas, but because even the more affluent parents they attract are the ones who consider education unimportant. The Government, in the last Budget, pledged to concentrate spending on such schools. Bringing class sizes right down in these would be an excellent way of focusing that commitment.

d.orr@independent.co.uk