A teacher with 40 years' experience – described as a "mother figure" by her pupils – has become the first to die a violent death on school grounds in 18 years.
Ann Maguire, one of the longest-serving and best-loved teachers at Corpus Christi Catholic college, Leeds, was stabbed to death in front of terrified pupils shortly before lunch on Monday.
A 15-year-old student at the school was arrested at the scene.
David Cameron described the events as "profoundly shocking" and Leeds police insisted it was an isolated situation and that they had worked hard to improve safety in schools.
But teaching unions warned that although violence in schools has not increased in recent years, the events highlighted the risk teachers face in their jobs.
Brian Lightman, of the Association of School and College Leaders, said it was "an isolated incident", but questions needed to be asked "to make sure every precaution is in place" to prevent such things happening.
In a press conference outside the school on Monday afternoon, Ch Supt Paul Money, Leeds District Commander, described the murder as "a very shocking and unprecedented incident for Leeds".
He said of the attack: "It involved a 61-year-old woman teacher being stabbed by a male pupil within the school building. The incident was witnessed by other pupils, who raised the alarm. The suspect was detained by school staff on the premises before police and paramedics arrived at the school. The injured teacher was treated by paramedics and taken to hospital, but tragically died from her injuries."
He added: "The incident itself was over very quickly and no other pupils or staff were threatened or injured. However, this has clearly been a very traumatic situation for those involved and we are working closely with the school and the local authority to ensure they are fully supported while they assist the investigation. Specialist detectives highly experienced in treating child witnesses sensitively are being used to interview them."
Apart from the Dunblane massacre in 1996, the last teacher to be killed at a school in the UK was Philip Lawrence, head of St George's Roman Catholic school in Maida Vale, north London. He was stabbed to death outside the school gates when he went to help a 13-year-old pupil who was being attacked by a gang.
Schoolchildren were expelled or suspended on 17,520 occasions for physically assaulting adults in 2011-12, according to the latest available figures.
This amounts to more than 90 a day across the academic year, although those figures have not changed dramatically in recent years.
Airport-style security arches that detect knives and guns have become an increasingly common sight at school gates, and in 2010, ministers handed new powers to headteachers to search pupils for weapons, drugs or stolen goods in a government drive to improve school discipline and crack down on violence.
Hilary Benn, the Labour MP for Leeds Central, described the incident as "profoundly saddening", but said he was not in favour of stringent security measures that would keep staff and pupils "behind high fences".
He told BBC News: "Schools are places of learning. We want our schools to be open – we don't want to lock pupils and staff behind high fences."
Outside the school, pupils revealed how a routine morning had ruptured. It was approaching lunchtime when pupils at Corpus Christi raised the alarm, shrieking as they ran for help.
Maguire's colleagues rushed to her side, some administering first aid while others held her attacker, witnesses said. One teacher called an ambulance as others went from room to room telling students to stay put.
The school's 1,000 pupils weren't immediately told the awful truth. "They said there had been a leak in the corridor and we couldn't come out," said Breon Morton, 14.
Another pupil, who did not want to be named, said: "I was in the science lab doing some science work and I just heard everyone screaming and running about and then we just got told to stay there."
It was 11.48am by the time police reached the school, which is on the Halton Moor estate 3.5 miles east of Leeds city centre. Forensic experts soon arrived, taping off the area that would soon become a murder scene. A 15-year-old boy from the school was taken into custody. "We were so shocked, no one could believe it," said Morton.
The school decided not to send pupils home, with police advising management it would be easier to keep the children safe and calm on school grounds. Normal lessons were cancelled, with students allowed to watch films on their laptops or talk quietly until it was time to go home.
Once it was hometime, pupils left school hugging each other, many with tears rolling down their faces. Nuns were on hand to offer comfort to those who needed it. Then began the steady stream of former pupils, many grasping bouquets and cards, who came to pay tribute to a woman many described as a "mother figure".
Nichola Davies, 34, had driven 35 miles to lay a bouquet after hearing the news on the radio. "I left in 1996, but I've never forgotten her. She was just amazing. She took the time for you." Maguire, she said, "was a hugger – she'd hug you, back in the days when you didn't get in trouble for that sort of thing."
Jefferson Barara, 18, wiped away tears as he told of his shock. "She was a friend to all of us. Even when we left after our GCSEs and went to college, she would check up on us and was always there for us if we had troubles. She didn't deserve to die. With many teachers you can't share your problems or tell them what's going on, but she was amazing. She was like a mother figure to a lot of us."
