A large proportion of pupils have separated or divorced parents, and this has a huge impact on daily life because of its effect on children's behaviour.
Children from broken homes are twice as likely to have most kinds of problems compared with children from intact ones, according to 1998 research by the Joseph Rowntree Trust. Of most relevance to teachers are the increased delinquency, lower IQ and poorer academic performance: crudely put and on average, it makes children less good learners and harder to control.
There is an especially high risk when the mother has gone, leaving the dad in charge. More than half of boys in this scenario will be delinquent children and in a staggering two-thirds of cases, graduation will result not in a degree but in an adult criminal conviction (compared with one-third if it is the dad who left).
More subtly, break-ups affect children's relationship patterns, making them more likely to be insecure in their dealings with teachers. In some, this takes the form of avoidance. Feeling rejected, they assume a haughty disregard for your social overtures or attempts at support. In others, a fear of being abandoned means they cling to you.
On average, a girl whose father left the family home before she was 10 comes into puberty six months earlier. Since early puberty increases the chances of a girl starting sex young, having multiple partners and of teenage pregnancy, this can damage her academic prospects. On top of that, as many male teachers can testify, such girls are a handful if their main interests are flirtation and seduction (of an absent father).
What parents are like when they are there is at least as important as whether they split. For example, it is not only separation that accelerates puberty.
Sons with anti-social dads are more badly behaved if he lives with them than if he does not, so it may be better for the boy if that kind of dad departs. Tellingly, children from intact homes where there are high levels of conflict are as likely to be delinquent as ones from broken homes.
When it comes to high achievement, there are plenty of exceptions.
Childhood adversity (not genes) is the major driver of genius: about a third of successful people in any given field suffered the death of a parent before the age of 15, according to American research. There are children who respond to parental break-up by becoming exceptionally able, academically or professionally.
For a perfectionist person, becoming the cleverest in the class is one way to make yourself feel good if you feel lousy. As a teacher, you may be delighted to have someone so fastidious in your class, but you may also worry about what all that perfectionism is doing to them.
If only they would rethink the purpose of school so that instead of grades the annual league tables measured how well pupils' psycho-social health has fared . . .
Divorce rates and other social disadvantages could be factored in to allow for differences in school populations. While teaching would still be important, and you might need some retraining, wouldn't it be great at the end of a year to be able to say: "Rates of depression and anxiety among pupils from broken homes in my class have halved this year"?
Oliver James's book "They F*** You Up: How to Survive Family Life" is published by Bloomsbury.