A study in the United States has compared the proportion of children in 1979 who were reported to have problems with their behaviour with a similar sample in 1996 - and found that there had been a sharp increase.
The survey is published as the political parties in the United Kingdom argue over how schools should handle what head teachers say is a growing problem of disruptive and violent pupils.
In the United States survey of 4 to 15 year olds in 1979, there were 6.8% identified as having behavioural problems, which by 1996 had risen to 18.7%.
The greatest single increase was in "attentional" problems, such as attention-deficit disorder and hyperactivity.
The original study had analysed a representative sample of children in Rochester, New York - and the follow-up study was based on a larger national sample.
Poverty
Among the factors which could have contributed to the increase, say researchers, was the rise in the number of children growing up in impoverished, single parent families.
Researchers, from the universities of Pittsburgh and Rochester, noted that children with behavioural problems were twice as likely to be in low-income families and boys were twice as likely as girls to have problems.
In responding to disruptive behaviour, the comparative survey showed the emergence of drugs such as Ritalin. In 1979, less than 1% of children with disturbed behaviour were treated with Ritalin-type drugs, a figure which had risen to over 8% by 1996.