At 11:48am today police were contacted by the ambulance service who were attending a report of a member of staff having been stabbed at Corpus Christi Catholic College, in Neville Road, Leeds.
The 61-year-old female member of staff was taken to hospital for treatment but was subsequently pronounced dead.
A 15-year-old male pupil was arrested in connection with the incident and remains in custody this evening.
Chief Superintendent Paul Money, Leeds District Commander, said: This is a clearly a very shocking and unprecedented incident for Leeds, which has understandably had a massive impact on staff and pupils at the school and on the wider community.
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. Specially-trained family liaison officers have been assigned to support the family and our sympathies are with them at what must be an incredibly difficult time.
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 that they are fully supported while they assist the investigation. Specialist detectives who are highly experienced in treating child witnesses sensitively are being used to interview them.
This is now a murder enquiry and, as people would expect, a full and detailed investigation is underway. We anticipate this will cause some significant disruption to the operation of the school but we will maintain close liaison with the school and the local authority to ensure that is kept to a minimum, although clearly the needs of the investigation will have to come first.
It is worth remembering that schools in Leeds are generally very safe places to work and study helped by the partnership approach we engage with as part of our safer schools initiative in many schools, including Corpus Christi, and right across the City.