The survey also found that twice as many teenagers in 1995 as in 1989 said there were gangs active in their schools, a development described as “unacceptable” by President Bill Clinton, who urged Congress to pass youth violence prevention measures and anti-gang laws he proposed a year ago.

Twenty-eight per cent of students aged between 12 and 19 said they had witnessed street gangs in their schools in 1995, compared with 15 per cent in 1989, the Bureau of Justice Statistics and the National Center for Education Statistics reported.

Four per cent said they had been physically attacked or robbed during 1995, up from 3 per cent in 1989 - an additional 270,000 victims, said Pascal D Forgione Jr, US commissioner of education statistics.

He said there was a close correlation between violence and gangs in schools. The report follows the killings of four students and a teacher at a rural middle school in Arkansas by two boys. One, the 13-year-old Mitchell Johnson, pretended he was part of a gang and wore red every day, the colour of the Bloods gang, classmates said.

But researchers add that other data suggest violent crime by juveniles peaked in 1994 and has declined since, a trend not yet apparent in the published statistics.