Police and the North East Ambulance Service launched an operation after staff at James Calvert Spence Community College’s Acklington Road site in Amble, Northumberland, made a frantic call to the emergency services.
A spokeswoman for Northumberland County Council said staff had been at the school for a training day and no pupils were on site.
The male teacher was rushed to the Accident and Emergency department of Wansbeck General Hospital where he received treatment.
It is understood the headteacher at the school was alerted to the incident after a note was sent saying he planned to end his life.
A source told The Journal: “All the staff are shocked that someone would try to take their own life on school premises.
“He was taken to hospital and he received treatment but it’s really upset people and his colleagues.
“Somebody needs to ask some questions about what has happened.”
The school was at the centre of a merger in 2011 when Amble Middle School on South Avenue amalgamated with the former Coquet High School on Acklington Road.
The merger had been proposed by governors of the Coquet Federation following concerns by falling numbers at both sites.
A Northumberland County Council spokeswoman said it was against policy to discuss individual members of staff but confirmed there had been an “incident”.
She said: “We can confirm that an incident took place at the school on Tuesday, which was a teacher training day and no students were in school at the time.
“It is not our policy to discuss the circumstances of individual members of staff.”
A Northumbria Police spokeswoman released a statement saying they had been called to the site and said there was no “third party involvement”.
She said: “We can confirm that on September 3 we received information from the ambulance service that a man had been taken to hospital for treatment to his injuries.
“The incident occurred at a school in Northumberland.
“Officers did attend and it was found there was no third party involvement.
“He was taken to hospital but there was no further police involvement.”
The teacher’s condition was last night unclear. A spokeswoman for the NEAS said: “We were called at just before 9am after concern for a male patient.
“He was taken to the Accident and Emergency department of Wansbeck General Hospital.”