A 15-year-old boy is being treated in hospital for stab wounds after being hurt during an incident at a secondary school, police said.
The incident took place at Blyth Jex School in Norwich just after 1pm on Friday during the school break.
The youngster, who has not been named, suffered wounds to his back after being
involved in a disagreement with another pupil, Norfolk Police said.
A 15-year-old boy had been arrested on suspicion of wounding, police added.
A Norfolk Police spokeswoman said: "There was some sort of dispute between two 15-year-old boys and one has suffered wounds to his back.
"We believe the wounds were inflicted by a small lock knife. The injured boy is being treated at the Norfolk and Norwich Hospital in Norwich.
"He is in shock but we don't believe his injuries are too serious and we are hopeful that he will be released from hospital soon."
A 15-year-old boy has been arrested on suspicion of wounding and is helping with inquiries, she added.
The head of Blyth Jex, Karen Topping, said: "There was an incident at the end of lunchtime today (Friday) when two Year 11 boys were involved in a disagreement.
"This is an incident that Blyth Jex takes very seriously as it is totally out of character for our school."
A boy has been suspended and an inquiry would be carried out into the incident, she added.