The teenager was stabbed by another pupil at the school

Police said the boy was stabbed three times in the chest and stomach with a knife at Allerton Grange High in the north of the city at about 0930 GMT.

He was taken to Leeds General Infirmary where he was in a stable condition.

A group of boys outside the school claimed the injured pupil had been stabbed in a revenge attack by a boy he had bullied.

One of the boys said: "He had done it because he got bullied. It was revenge."

There was a gang culture at the school and a problem with bullying Former pupil

A 16-year-old Year 11 pupil at the school said: "It's really shocking. Not many kids around here carry knives. We're just really surprised."

A 20-year-old former pupil, who did not want to be named, said there was a problem with bullying and gangs at the school.

He said: "My younger brother was bullied. There was a gang culture at the school and a problem with bullying. The teachers found it hard to deal with."

Parts of the school, described on its website as a "thriving, all-ability, multicultural school", have been cordoned off as police continue their investigations.

Detectives said the stabbing was not being treated as a racial attack.

School 'calm'

Richard Morris, chairman of governors at Allerton Grange, released a statement through the city's education department which said: "We cannot comment on this morning's incident as it is a matter for the police.

"The school is calm, lessons are proceeding as normal and we can reassure families that it is a safe environment for their children.

"Our thoughts and hopes are focused on the young person in hospital."

Worried parents gathered at the school gates as they heard the news about the stabbing.

One mother, whose daughter is a pupil at the school, said she believed there had been trouble at the school recently.

"I heard that there was some fighting at the school yesterday," she said.