Four separate fatal shootings by pupils in rural American schools have severely jolted a society that had perceived itself as making strides toward curbing violence by children.

Even as the nation searched for explanations, experts called the killings sad but random deviations, not symptoms of a sudden youthful homicide epidemic.

Mitchell Johnson, 13, and Andrew Golden, 11, donned camouflage clothing and opened fire at an Arkansas school last week, killing four fellow pupils and a pregnant teacher who was shielding another child from the bullets.

It was the fourth such incident in five months. In October, two pupilswere shot dead in Mississippi; in December, a boy opened fire on a prayer circle at a school in Kentucky, killing three and wounding five; and, also in December, two children were fatally shot by a classmate at another Arkansas school.

“Is this an escalation of the youth violence trend that started in the mid-1980s, which had been ebbing? The answer is, no,” said David Kennedy, a senior researcher at Harvard who specialises in youth violence prevention.

“This stuff we’ve been seeing in the past couple of months is none of that. It’s also not, in any way we can figure out, rooted in anything that would create a lot more of it. There’s no common thread.”

Juvenile crime in America has actually been falling. Only one school in 10 reported a serious crime last year. And each of the three recent schoolhouse shootings followed different patterns. One of the alleged youthful killers reportedly was inspired by a scene in a film; another was part of a teenage cult and Mitchell Johnson apparently was angry over a break-up with his girlfriend.

Still, President Clinton immediately ordered a study of the incidents, and the US Senate quickly passed legislation to make sophisticated security systems available to schools. One lawmaker proposed a measure that would hold adults responsible when their guns are used by children to commit a crime.

If anything, officials said, the shootings demonstrate again that there are too many guns in the United States, and that they are too easily available to children. Andrew Golden allegedly stole the seven guns used in the Arkansas killings from his grandfather’s collection. Yet he also owned a gun of his own, since it is legal in Arkansas for children to have guns other than handguns.

Nationwide, there are an estimated 200 million guns in private hands. Nearly 8 per cent of American high school students report carrying a gun within the previous 30 days. In 1995, the most recent year for which the figures are available, more than 5,200 children and teenagers were killed by guns, according to the US Centre for Disease Control.

“To the extent that there’s a trend here, it’s the availability of guns in this country,” said Jack Calhoun, director of the National Crime Prevention Council.

Other experts fret that children also are increasingly desensitised to violence by television, movies and video games. In one of the most popular TV shows, the animated South Park, for example, third-graders commit or are the victims of a killing every week. The American Psychological Association estimates the average American 18-year-old has witnessed 200,000 acts of violence on television, including about 20,000 murders.

Mitchell Johnson liked to imitate the characters from the MTV programme Beavis and Butthead, his friends said, and pretended he was in a gang.

“The stuff is out there. It’s in our culture now,” said Mr Kennedy. “It’s not just in the movies. It’s on the news.

“The world of 1998 is a world in which kids can lay awake at night and think dark thoughts about killing lots of people and it’s not as out of reach as it has been in previous decades,” he said. “The country’s just different today, and there’s no going back.”

Jon Marcus