Yet these aspects seemed to relate to learning difficulties. In the playground Sam would lash out suddenly and be unable to give a reason. Much to the surprise of the school, the educational psychologist found that Sam’s intelligence was normal but referred him to a child guidance unit.

It emerged that soon after his birth, Sam’s father went to prison and was never seen again. The family were homeless until Sam’s mother took up with another man. Soon she had a new baby, whom she adored to the exclusion of Sam, who fell prey to his stepfather’s sadistic sexual behaviour. After a while, Sam’s maltreatment became apparent and the stepfather was jailed. Sam was put into care.

Thereafter, the family re-formed and separated with each successive return of the stepfather, new baby, and removal of the abuser. Six step-siblings and many spells in care later, Sam was, unsurprisingly, finding it hard to trust life. The therapist helped him reveal that behind his “dumb” facade lay aching a deep sadness.

Yet, once Sam’s feelings of despair were revealed and accepted, he made huge leaps in his schoolwork. No longer one of the “slow set”, he became able to make friends and develop strategies for dealing with life.

Maureen was unfailingly cheerful and bright. Her teacher would have been amazed to hear her called depressed. Yet she was struggling daily with the burden of a mother mourning the death of her son. Mother could not get out of bed until 3pm, yet forbade any mention of the dead boy. Maureen’s own feelings of grief and bewilderment were simply inadmissible and her only recourse seemed to be the establishment of a “false self”.

So much energy went into this false Maureen that the true child was unable to concentrate on her schoolwork. Things reached a critical stage when Maureen, about to go into secondary school, developed blinding headaches. Her brother had died from meningitis in his first year at secondary school. The doctor found no organic cause for the headaches and called in a psychotherapist. She brought the family together and simply asked the parents to tell their child how hard they had found it to lose their son and how worried they were that Maureen would suffer the same fate. The headaches disappeared and Maureen began to look forward to school.

Depressed people, children and adults, may not necessarily appear sad. As Muriel Barratt, an expert on this subject, has said, depression is a “hidden factor”. Sufferers may feel low all the time, but they may also seem to be at the opposite extreme, of hyperactivity. However depression manifests itself though, it is likely to interfere significantly with cognitive organisation. A very few children may choose a flight to the intellect to avoid their emotions; most find it hard enough keeping intrusive misery at bay without also learning their times tables.

Teachers have an important part to play. With a child like Sam, who has not had a secure childhood and cannot trust adults, the teacher needs to show, by consistent and positive demeanour, that she or he recognises the child’s problems but has faith in his ability to engage with them - a faith which the child lacks. With a more secure child like Maureen, it is still important to show that emotions need not be discounted. Not that the classroom should become a wailing wall or encounter group, simply that there is due recognition for the child’s situation.

Some theorists on depression have hypothesised that a hostile glance from a teacher can activate negative brain chemicals in a child who has already been damaged in early life. It is not necessary to go that far to understand that teachers can help children build the self-esteem which depression has eroded. Bullying, teasing and sarcasm are damaging; fairness, respect and merited praise are healing.

Depression is, literally, maddening: in adolescence children try to gain short-term relief from their negative feelings about themselves by turning to drugs, criminality or truancy.

Longer-term outlets can include recurrent psychosomatic illnesses. Most hopelessly, the false self can be erected into a flat and shining facade which admits of no intimacy at all.

One sample quoted by Ms Barratt suggests that 71 per cent of depressed children were underachievig in school. Her solution is for teachers to become “educational attachment figures”: to remain well-disposed toward such children and confident of their worth even in the face of challenging or withdrawn behaviour. Yet another superhuman demand on hard-pressed professionals?

Perhaps, but as everyone who has been depressed (and who hasn’t?) knows, all that is really needed is to know that someone understands and does not blame. Pity, as much as impatience, reinforces low self-esteem; recognition repairs it.