The prime minister has expressed his horror at the death of a teacher, who was stabbed at a school in Leeds.
Anne Maguire had been a teacher at Corpus Christi for more than 40 years
Chief Supt Paul Money of West Yorkshire Police said teachers at the school held the 15-year-old suspect until officers arrived, shortly before midday, and he is now being held in custody although he has not yet been charged.
He said: "A 15-year-old male pupil from the school was detained at the scene by other members of teaching staff immediately after the incident occurred.
"The alarm was raised by students in the school, some of whom witnessed the offence."
He said a knife had been recovered and added: "There were a number of stab wounds to the lady in question."
Leading politicians have condemned the death of the popular 61-year-old teacher as "appalling".
"This is a profoundly shocking, indeed absolutely appalling, incident," David Cameron said. "All our thoughts are with the teacher's family, with the school and all the pupils who study there.
"Everything that can be done to help this school get to the bottom of what happened will be done. I think that we have to wait for the investigation to see what exactly happened."
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Teacher stabbed in Leeds
Labour leader Ed Miliband said: "The killing of Anne Maguire was an appalling act. My thoughts are with her family, the school and those pupils who witnessed the attack."
Dean Sean Quigley said the Corpus Christ Catholic Church next to the school was opening for people in the community.
He confirmed Mrs Maguire had been at the school since she first went on teaching practice as a young woman and had celebrated her 40th year at the school last year.
He said: "She was just a wonderful, caring person. She was head of year 11 for in excess of 10 years and she was just so patient in her pastoral work.
"She was held in such immense esteem. She taught the grandparents of some of these children here today."
He said the community was in shock and he was thinking about her husband and children.
Speaking outside the school, 16-year-old pupil Georgina Kilroy said: "I don't know anyone who didn't like her. She was spot on. You couldn't ask for a better teacher."
Georgina said her teacher broke down when she told the children the news. She said that before then they were told a teacher had gone to hospital but lessons continued.
Flowers left at the gates of Corpus Christi Catholic College
Nichola Davies, 34, broke down as she tried to explain why she had driven 40 miles from Goole to pay her respects.
Mrs Davies, who left the school in 1996, said: "She was just amazing. She was such an incredible lady. It's just so heartbreaking, it really is."
Katie Gallagher, 15, said she was in a nearby room when Mrs Maguire was stabbed.
She said: "I heard her scream. I was in a meeting at the time but I heard it."
She said the incident happened in a normal Spanish class with around 30 children witnessing what happened. Everyone in her class burst into tears when they were told about the teacher's death.
Hilary Benn, 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: "Most people are good and most people try and do the right thing.
"This is not representative of the college, of the community that surrounds it, the families that send their children to school and the city itself. But it is profoundly saddening."
Hundreds of pupils, former students and their parents crammed into the pews of the Corpus Christi church on Monday evening.
There was no formal service but teenagers hugged each and some lit candles as they wiped away tears.
A few yards outside, scores more youngsters gathered around the floral memorial to Mrs Maguire while some teenagers pinned photographs to the railings, with teddies and other memorabilia.
One note said: "You inspired countless generations. You taught four generations of our family and you were simply a totally fantastic teacher, always caring and always there to make us smile (even if you were speaking Spanish)."
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