One in 10 children now suffers mental health problems, but schools are receiving little help to deal with them.
An Audit Commission survey of nearly 6,000 schools in England shows that two out of five say the support they receive from local child and adolescent mental health services is poor or very poor.
Heads and health experts cite poverty, the loss of extended families, the testing regime, drugs and peer pressure as among the factors behind mental health problems.
Latest government figures show such problems affect 850,000 5- to 16-year-olds. Behavioural disorders are the most common manifestation. Other problems range from mild anxiety to psychosis.
Angela Piddock, head of Wilberforce Primary in Westminster, London, said: "The prevalence of mental health problems in schools is very high. The ever-widening gap between the haves and have-nots makes many families stressed and that filters down to the children."
In the past four years, pound;400 million has been invested in child mental health services, but this has done little to check the problem.
The Government has admitted there are "gaps" and this week announced that 25 pathfinder authorities would pilot new methods, with early intervention for problem pupils or those at risk.
The Marlborough Family Service in Westminster has developed a model involving parents, teachers and specialists, which has been held up as an example.
Particularly difficult cases are handled in-house, where techniques include using heart-rate monitors to show children how stressed they are becoming. The centre also runs outreach clinics.
Brenda McHugh, joint centre head, said: "We try to allay the fears of people who think mental health means madness. Once you get families working in school, change occurs quickly, and because you are not just dealing with the pupil on their own, solutions tend to stick."
Neil Dawson, joint centre head, said: "Schools need to get beyond the idea that a naughty child relates to a bad family and start seeing families as a resource for change."
Michael Matthews, head of Barrow Hill Junior School in St John's Wood, London, said he had noticed an increase in mental health problems among pupils in his 30 years of teaching. "We have been so lucky here because the centre is superb," he said. "But it is the exception and it needs to be replicated."