Teenage girls are the most likely to cut, poison or burn themselves as a way of coping with their troubles, according to psychologists in North Lanarkshire.
"When they see the blood running from their arm, they see the badness running out of them," Karen Telfer said.
Initially, there was a calmness and sense of well-being before pain, guilt and shame set in. Young people who harmed themselves did it to relieve their feelings, as a form of self-punishment and as a way of controlling their lives by making themselves unattractive to an abuser.
It could also be a distress call, a cry for comfort or a move towards suicide.
Mrs Telfer said that personal trauma appeared to be the trigger for self-harm and the key factors were relationships in the family and among peers. Teachers had to find out the reasons before they could begin to turn round the sadness and grief.
"Eighty to 90 per cent of adults who deliberately self-harm say it is a response to childhood experiences," Mrs Telfer said.
Catherine Cruickshank said North Lanarkshire schools had notified psychologists of 85 pupils who harmed themselves between 1999-2002 - 25 in primary and 60 in secondary. The peak years were S3 and S4. Boys feature more in primary figures and girls in secondary. Meanwhile, the incidence of suicide was rising with four deaths in recent years.
Tom Lowe said abuse - including bullying - and relationship conflicts were the two main causes of suicide. Young men found it particularly difficult to ask for help.
"Schools run memorial services for pupils who die in accidents but there is a huge debate around suicides. The trauma for pupils is much more significant and the rumours will start about why they committed suicide. So the school has to be proactive," Mr Lowe said.
A schools' pack on Critical Incidents is available from North Lanarkshire psychological services.