“It was just a little boy who had problems none of us knew about,” he said. “I would hope that we can go about our business with the idea that the vast majority of kids are just kids.”

But a spate of schoolyard shootings has added an onerous burden to US schools and teachers : what to do about violent threats from students, after evidence that talk can turn deadly?

Since October, three small-town American schools have suffered at the hands of armed pupils. In all three it appears there were warnings signals - threats of killing and revenge. In Springfield, 15-year-old Kip Kinkel apparently read from his journal in class about his plans to “kill everybody”, and was known to be obsessed with weapons.

Last week, Kinkel was caught with a gun at school , interviewed by police, and released to his parents’ custody. Within hours, he allegedly shot them both dead, went to school and opened fire, killing two and wounding 20.

“If we detained every student who said they were going to kill someone on our campus, we would have a large number of students detained,” said Springfield schools superintendent Jamon Kent.

But schools have already stepped up anti-violence measures, and toughened the response to threats. Solutions include peer intervention, metal detectors and security guards.

In Kentucky, a schoolboy was arrested for threatening to kill his baseball coach. In Seattle, a six-year-old boy who made threats and mentioned guns was put under permanent adult escort.

Random shootings by pupils are beginning to look like copycat crimes. Mr Durfee said: “It worries me that some other school is going to endure what we just have because some kid’s going to see this in the media.”

Teachers, he said, “are always careful, trying to know the personalities you are dealing with”, and may be especially watchful now. “I’ve never been threatened and I’ve never heard of someone being threatened,” he said. “I think we would be wrong to go in with the premise that kids are going to do something bad.”