A long-term study of children with behavioural problems has found that early intervention by parents can make a significant difference.

The research in the United States tracked families for 25 years in an attempt to find the impact of training parents in ways of controlling the behaviour of disruptive toddlers.

The parents of children who had begun to show aggressive and anti-social tendencies by the age of two were given training courses in how to impose discipline.

The study, which is to be published by the United States Education Department, says that the early efforts to improve children's behaviour brought about long-term benefits.

Instead of predictions that such disruptive children would lead down a path of educational underachievement and delinquency, there were indications that the children had grown into socially adjusted adults.

"The long-term effects of them not being treated or poorly treated are pretty devastating," said Phillip Strain, research leader and a professor of educational psychology at the University of Colorado, Denver.

The children tracked in the study were not just naughty or mischievous, say researchers, but were more severely disturbed - showing violence towards parents and other children and having tantrums that lasted over an hour.

Parents were taught how to respond to their children's violent outbursts. The strategy involved teaching parents to calm down before punishing children, making children make choices about their own behaviour, setting clear rules and praising good behaviour.

The study will be examined by the Education Department at a time when there is widespread concern about the threat of violence among young people.

After the gun attack at Columbine High School in Colorado last year, there have been efforts across the United States to find ways of developing 'early warning' systems for detecting violent behaviour among pupils.

Along with improved security, there have been attempts at psychological profiling to identify potentially dangerous pupils and programmes to reduce violence and aggressive behaviour.