Despairing headlines suggest that aggression in the classroom is getting worse, violence and intimidation are "endemic", and even primary school pupils throw toddler tantrums if they fail to get their own way. Teachers coping with bad behaviour increasingly blame parents for not socialising their children properly.
The evidence suggests that teachers are right. Experiences of harsh or neglectful parenting, or early separation from the parent or attachment figure, play a significant part in anti-social behaviour.
The comedian Billy Connolly experienced all three. His mother neglected him as a baby, and then finally "closed the door and never came back" when he was only four years old. His resentful Aunt Mona then took over, hitting and verbally abusing Billy, and sometimes humiliating him by "grabbing him by the back of his neck and rubbing his soiled underpants in his face". Billy in turn became a reckless, aggressive child who played dangerous practical jokes on other children and would give others a "severe seeing to" when he was provoked. At school, he demonstrated learning difficulties and tended to overreact to any criticism.
Faced with such badly behaved children, teachers are sometimes tempted to share the tabloid newspapers' view that parents are too "indulgent", letting them get away with staying up late, swearing and playing aggressive video games. But a kinder way of looking at is that they are mostly parents who can't regulate their own emotions well enough to pass on such capacities to their children.
Billy's mother was only a teenager herself, isolated and depressed, bringing up two young children on her own. She fits the typical profile identified by the Canadian aggression researcher Richard Tremblay: of low income young mothers, who smoke during pregnancy and are unsupported by good personal relationships.
He believes these are the parents most likely to fail to teach their children to regulate physical aggression.
However, I don't believe that such problems are confined to the lower socio-economic groups. I have also had many middle class families in my consulting room who struggle just as much with managing their children's behaviour.
When I have got to know any of these mothers or fathers better, I have usually discovered that the story is that their own parents were emotionally unavailable or unsupportive in some way, and they find themselves unsure how to forge a strong bond with their baby or toddler.
It is this lack of satisfying emotional connection that is the real culprit. Early relationship difficulties not only affect a baby's psychological well-being, but also his or her brain, passing on poor regulation down the generations.
This means that what happened to Billy is likely to have had an impact on his physiological and neurological development. The kind of early stress he experienced can lead to an overload of the stress hormone cortisol, and the closing down of cortisol receptors. Eventually, as children like him become habituated to distress, the stress response itself may "down- regulate" and become less reactive, instead showing "spikes" of rage. This low baseline cortisol has been linked with early anti-social behaviour.
Chronic exposure to cortisol can also be toxic to the areas of the brain loosely referred to as the "social brain", during early development. And just as stressful relationships can handicap the development of the social brain, it is warm, attentive relationships that provide the optimum conditions for it to flourish and make neural connections.
One area called the orbitofrontal cortex, in particular, which normally starts to function by about 18 months, plays a key role in self-control and learning empathy for others.
From late toddlerhood onwards, the maturing orbitofrontal cortex can start to exert some "top-down" control over behaviour. It does this by laying down neural pathways that connect it to the rapidly reacting, impulsive areas of the sub-cortical brain (such as the amygdala). Well-loved and respected adults are in a strong position to help their toddlers to establish these pathways. But when parents can't model self-control in a consistent way, and don't encourage the child to achieve self-control through techniques such as self-distraction, it is unlikely the child will acquire them.
Grazyna Kochanska, professor of developmental psychology at the University of Iowa, has found that toddlers who can't manage what she calls "effortful control" are the ones who are most likely to become hyperactive, anxious or badly behaved later on.
In fact, the earlier such problems start, the more predictive they are of anti-social behaviour in adulthood. The only sensible conclusion to draw is for intervention to start as soon after birth as possible, as the Government is beginning to recognise.
However, teachers should not despair of making a difference to their pupils, however difficult their home lives and however bad their behaviour. Throughout their time at school, children are doing a great deal of emotional learning, while their neurons still connect relatively rapidly. Despite his difficult start in life, Billy Connolly learnt to use his aggression creatively rather than destructively.
Positive long-term relationships of any kind - in Billy's case, with his older sister, with a man he met through the Scouts who took a fatherly interest in him, and with teachers he admired - can make new pathways in the brain available, enabling different paths to be taken in life.
Sue Gerhardt is a psychoanalytic psychotherapist and author of Why Love Matters
Kochanska, G., et al (2008) A developmental model of maternal and child contributions to disruptive conduct: The first 6 years, Journal of Child Psychology and Psychiatry (eprint before publication). www.ncbi.nlm.nih.govpubmed18684154
Kochanska, G., amp; Knaack, A. (2003) Effortful control as a personality characteristic of young children: Antecedents, correlates and consequences, Journal of Personality, 71:6, 1087-1112
Tremblay, R. (2004) Physical aggression during early childhood: Trajectories and predictions, Pediatrics, 114:1, e43-e50 (online publication)
Violence and what to do about it, The Wave Report, Wave Trust, (2005) www.wavetrust.org.