Thomas Hamilton's dreadful crime at Dunblane primary might have been prevented if he had received treatment during adolescence, a conference on self-inflicted injuries and suicide among young people heard this week.
Peter Wilson, director of Young Minds, the mental health organisation which this week launches a book on mental health in schools, said: "We have got the evidence but people find it difficult to fully believe."
Stopping crimes such as Hamilton's meant finding resources in schools to allow time for teachers to work with adolescents on personal and social development.
"There are many lonely, isolated people out there like him. His kind are not uncommon," Mr Wilson warned. "There are people who, for various reasons, have great difficulty in dealing with failure. It is an affront to their sense of dignity and they are consumed by the need to wreak revenge. It is something they cannot let go of."
In an average secondary school of 1,000 pupils, 50 might be seriously depressed and suffering from low self-esteem. They might have eating disorders and problems with relationships. More widely, one in five young people could be considered to have a mental health problem, reflected in emotional and behavioural difficulties.
Mr Wilson said: "Young people have to deal with a bucketful of preoccupations in their teens. Growing up is difficult and teenage life is not simply a bag of fun. All young people are preoccupied with their bodies. In their teenage lives, their minds are having to cope with the repercussions of puberty and the demands made on their sexuality."
Childhood had an enormous significance in determining a young person's ability to cope with the pressures. Mr Wilson told the Children in Scotland conference in Edinburgh, two days after the Dunblane tragedy, that around 600 young people under the age of 25 in England and Wales committed suicide every year and 15,000-20,000 attempted suicide.
In Scotland, around 170 young people take their lives and 15 per cent of those are aged 15 or under. Some 2,000 callers to Childline say they are feeling suicidal.
Carole Moore, Children in Scotland's special needs officer, identified increasing mental health problems among the young. "For young men, a major issue is underachievement in schools. They are therefore less able to take part in the labour market and lose their self-esteem," she said.
One in five young people were depressed by the age of 19 and more males were committing suicide.