The crunch came, literally, after 16 successful years. Mary had been given a notoriously difficult class at a primary school in the Home Counties where she had been teaching for the previous six years. Every day was a battle to keep order and there were eight especially aggressive youngsters whose mission in life seemed to be to disrupt other pupils and make teaching impossible.
The worst was pupil was a nine-year-old, hyperactive, a ringleader. He wasn't getting the attention he needed in a fairly large class, Mary says, and took out his frustration on everyone else. He would wander around the classroom, throwing crayons at other children, scribbling on their work, swearing and shouting. On more than one occasion he threw a pair of compasses across the classroom.
Mary had put him at the front to keep an eye on him and was trying to get him to read. He persistently refused and, after endless cajoling, suddenly went out of control. "He just went red in the face and went berserk," Mary recalls. "He was really being aggressive, shouting and swearing, and suddenly he picked up a chair.
"At first I thought he might smash it against the wall. But the next thing I knew he hurled it straight at me and for a split second all I could see was a heavy wooden chair flying through the air in my direction.
"Luckily I managed to dodge so it didn't hit my head. But it caught me square on the leg. It was really painful, but I managed to hide my feelings and told him to go straight to the head's office."
Another time, a boy was returning from the toilet and banged the door against a pupil's head. Mary went to try and sort things out when, to her dismay, she found herself subjected to the same treatment. "He waited until I was near enough then suddenly swung the door towards me. It hit me on the side of the head and stunned me for a few seconds. It could have knocked me out," she says.
In the third episode Mary was kicked in the leg. The attacks left her badly bruised, but they were also having an effect on her general health. She started suffering migraine for the first time in her life. She couldn't sleep and suffered from depression. "On more than one occasion I had to stop the car on the way to school because I was physically sick," she recalls. "I felt absolutely awful."
The violence was part of a larger problem. Mary felt was was being victimised by a headteacher who wanted to get rid of her. She contacted her union but says it offered little practical help. Finally she went sick with what amounted to a nervous breakdown.
That was two years ago. An application to an industrial tribunal was unsuccessful and there is little prospect of returning to the same school. The violence, she says, was destroying her self-confidence and self-esteem.
"When you find yourself being attacked by a child who you are supposed to be teaching, you feel it's all wrong. Nothing makes sense and you feel you can't go on. And you realise that you're in real physical danger. I was lucky, I just suffered bad bruising. But it could have been a lot worse. "
After several years in industry, a change of career was proving successful move for Chris, who had settled into a comprehensive school in the south of England and passed his probationary year. He was enjoying teaching and felt a sense of achievement in helping his pupils get good results.
Then a confrontation with a 14-year-old boy put an end to his new career. That was two years ago. Chris is still overcome by uncontrollable shaking and has to fight back the tears when he tells the story. "I wanted to do the best for the pupils and they were eager to learn," he says. "But there was one boy who just refused to pay attention and was continually disrupting the class.
"On the day the attack happened I was teaching in the science lab and I had to move him because he was being so disruptive. So he just sat with his back to me. I had to fetch a book from the prep room and when I returned he had gone.
"But a few minutes later he returned with his mother. She walked up to me shouting insults and swearing. She slapped me on the face and my glasses went flying across the room. Then she hit me again. There was nothing I could do. I couldn't hit back. But the worst thing was that this was all in front of the class. I felt shocked and completely humiliated."
The psychological effects of the incident included panic attacks, complete loss of confidence and depression. Chris was forced to take sick leave. He went to his doctor and was given anti-depressa nts and sent for counselling, which he found very helpful. "It's good to feel there is someone who will listen to you," he says. "It helps you to feel more relaxed and to get it off your chest."
He has not suffered any physical injury. But the real damage has been done to his dreams of teaching children and helping them make the most of their opportunities. "I never imagined anything like this could happen," he says. "I was so keen to help the children. The majority of them were very keen to learn and it was unfair that they were being disrupted by one other pupil.
"Now I don't think I will ever be able to go back to teaching. I will have to live with the trauma for the rest of my life."
Hazel Spence-Young was an experienced teacher at the Frederick Bird primary school in inner-city Coventry. It was a challenging job, and there was one pupil in particular, a 10-year-old boy, who was hard to handle. "There were a number of children with problems," says Hazel, "but this one was especially disruptive. He had been a law unto himself and nothing had been done to address his problems. He had not completed his assessment for the morning and had prevented several other children from completing theirs. So I told him to stay in class and complete the test.
"We had just moved into a new school and the safety railings hadn't been put up. He threatened to run out of the school as he had done a few days before when another member of staff had spent an hour trying to find him.
"He wouldn't listen to me and just stamped out of the room and headed towards the door which went straight out into a busy road.
"I was trying to be non-confrontational but he was swearing and shouting abuse. He started lashing out, kicking and punching. It was a huge temper tantrum because he couldn't get his own way. He started head butting and punching and hit me three times very hard under the chin. My head snapped back and I knew then I had been hurt."
Hazel was rescued by other staff and taken to hospital where whiplash-type injuries were diagnosed involving damage to the nerves in her neck. She spent three weeks in a neuro-surgical ward and was put on powerful drugs.
Two years after the attack, in constant pain and unable to lift objects and barely able to write, Hazel took early retirement on health grounds and has been told she will never work again.
But she decided to fight her case with the backing of her union, the National Association of Schoolmasters Union of Women Teachers. She took Coventry City Council, her employer, to court on the grounds that her attacker was a known danger and that the council should have provided a safe working environment. Hazel accepted a record #163;82,500 in an out-of-court settlement. The council offered more if she would sign a gagging clause agreeing not to speak about the case. But Hazel wanted to be able to speak out for the sake of other teachers.
"It all needed to be brought out into the open," she says. "Teachers need to know that they don't have to put up with being put in such a dangerous situation. They shouldn't have to face violent children in their classrooms."