A welfare officer has been stabbed in a secondary school by a pupil using a kitchen knife.
A 16-year-old girl was arrested on suspicion of attempted murder following the incident in an office at Winterton Community Academy, near Scunthorpe, North Lincolnshire, on Monday morning, Humberside Police said.
The 61-year-old support worker was taken to hospital but her injuries are not life-threatening, officers have said.
Speaking outside the school, which is at the end of a quiet cul-de-sac in the rural village of Winterton, Chief Superintendent Christine Wilson said staff had told her the weapon involved was a small kitchen knife which was "highly likely" to have been taken in.
Ms Wilson said the school had no history of violent incidents and it remained open.
But a steady stream of parents took up an invitation from headteacher Gareth Morris to collect their children following the incident, which happened just before 9am.
Ms Wilson said her officers responded to a "fight" in an office in the school and stressed the incident did not happen in a class.
"It happened in an office in the school, so all of the rest of the children were completely safe," she said. "They were all in their separate classrooms.
"And it is, obviously, a very rare and isolated incident.
"I can't think of another incident that's happened like this in my time as a police officer.
"We want to reassure parents that their children were safe at all times."
Ms Wilson said she did not yet know the exact injuries the woman suffered.
She said a police community support officer would be present in the school for the rest of the week.
She said: "We've not ever been to an incident at the school before. The school has never had a teacher assaulted by a pupil before.
"So it is extremely rare. It was reacted to very quickly by the school and also local officers."
Headteacher Mr Morris said: "We are keen to reassure parents and the community that this is an isolated incident and that the school remains open.
"We will support our staff directly affected and will be keeping parents updated throughout the day."
Mr Morris is quoted on the website as saying: "Our pupils live in Winterton and a number of surrounding villages.
"Many of them travel some distance to school because parents have chosen our school instead of one more local to their home. The school is, therefore, popular.
"We are also a caring community, recognising that each child is an individual whose needs must be attended to and whose talents must be developed."
According to the school's website, the academy has "made an incredible leap forward over the past couple of years", citing an Ofsted report which progressed from a rating of "special measures" to "good with outstanding features".
The incident will again raise questions about staff safety in schools.
Spanish teacher Ann Maguire was fatally stabbed by 15-year-old Will Cornick as she taught a class at Corpus Christi Catholic College in Leeds in 2014.
And Vincent Uzomah was stabbed in the stomach by a 14-year-old boy in a racially motivated attack in front of pupils at Dixons Kings Academy in Bradford in 2015.