In autumn 1994, 16-year-old Andy Bray wrote a letter to two friends in his former Spanish class urging them to “continue the work that I struggled so hard to begin . . . drive Senorita Cocina over the edge.”

The letter continued: “I am afraid now that I am gone, the class will no longer be disruptive and may even begin to do their homework. This cannot be permitted to happen . . . cuss them out in Spanish and cause disruption. To frighten teacher, speak each day about different methods of murder.”

Senorita Cocina was the class nickname for teacher Frances Cook. When she seized the crumpled letter from a student, she saw red.

Then she saw a lawyer. Citing a year’s worth of harassment and threats by Bray, mostly in Spanish in front of the class, she sued him.

The battle of wills in remote northern Kentucky, between a hulking 6ft 2in farm boy and a doughty 5ft 9in 55-year-old teacher, began in her classroom in September 1993. It ended last month in a four-day trial.

Bray, now 17, starts college this term owing Mrs Cook almost Pounds 23, 000 in damages. A sympathetic jury awarded her Pounds 16,000 in punitive damages, Pounds 3,000 for emotional distress and nearly Pounds 2,000 for medical expenses.

While teachers have filed criminal complaints before, and in some recent cases have taken out restraining orders against pupils, Mrs Cook’s victory in a civil court appears unique. To American teachers - who often complain of verbal, physical, and judicial abuse - she has emerged a hero.

“We felt he was responsible for his own actions,” said juror Isaac Mullins. “What he did was wrong. I hope it sends a message that students can’t do this to teachers.”

In a neighbouring Kentucky district, school superintendent Jon Draud distributed copies of newspaper articles about the case to pupils returning this autumn. He said it was to inform them that they would face some very serious consequences for unruly behaviour.

Mrs Cook’s central claim was that the system did not help her. She reported Bray to the principal at Campbell County High and also spoke to his mother, but he dogged her for a year. He received just 40 minutes’ detention for writing the threatening letter.

Bray’s lawyer maintains he was just an obnoxious teenage boy, bright but immature, a harmless jokester, and it was Mrs Cook who lost control. When the class learned the Spanish word matar, for “to kill or murder”, Bray set them roaring with laughter by using it in sentences. He admitted misbehaving but denied threatening her life.

But Mrs Cook testified that Bray blurted out in Spanish: “I am going to kill you, Mrs Cook.” He used matar to talk of killing women, teachers, and redheads, she said.

When she took him into the corridor and asked him why he said he wanted to kill her, he answered calmly: “Probably because I do.” Mrs Cook believes Bray threw eggs at her house at Halloween and made nuisance calls to her home.

She said she wanted to believe it was just his warped sense of humour. But it was the letter, with the hint that he could pursue her even after he had left her class, that finally terrified her. She lost weight and couldn’t sleep. Mrs Cook has since retired and is undergoing treatment for post-traumatic stress disorder. Bray was finally expelled.

When his mother testified in court, he wept. In Kentucky anyone over the age of reason - possibly as young as six or seven - can be sued. Bray’s lawyer plans to appeal as his client could go bankrupt.

The issue of violence in schools is very much alive in the US, particularly in Kentucky. Two years ago a pupil shot and killed a teacher and a school keeper. The superintendent overseeing that school, Ross Julson, moved to Mrs Cook’s school shortly before she brought the action.

“What I found out from that case is that you don’t know what the threat is until it happens,” Julson said. “Even an implied threat can turn out to be a real threat. Almost all of the time it turns out to be nothing but the 1 per cent makes you understand that you better take the other 99 per cent seriously. ”

This week the American Federation of Teachers launches a new campaign for codes of conduct and academic achievement in schools, to lay down the response to disruptions and dangerous behaviour. Schools appear to be toughening up on disruptive pupils - just as politicians are with criminals.

According to the AFT, one in five US teachers has been attacked at school, and about a third have considered leaving the profession, because of violence and intimidation. A recent Justice Department survey found that one out of every five high school students owns a gun.