A teacher and 14 children needed hospital treatment after a pupil sprayed them with cleaning liquid during a schoolyard fight.
The 14-year-old boy was involved in a brawl with another pupil at Newcastle's West Gate Community College on Monday when he sprayed the liquid from a bottle.
Police said the youth, who was arrested at the school, had apparently found the cleaning fluid in a skip.
The teacher and pupils, aged between 12 and 14, were taken to nearby Newcastle General Hospital and released after treatment for minor facial injuries and skin irritation.
The boy, who is still being questioned by police, has been excluded from the school following the incident.
Northumbria Police said the teacher was splashed in the face as he tried to break up the fight.
Superintendent Steve Neill said: "This appears to have been an isolated incident. The substance appears to have been a mild cleaning fluid used to clean pipes in pubs which the 14-year-old found discarded in a skip. It appears to have been obtained purely by chance.
"The substance was discharged during a fight between the youth and a fellow pupil.
"A number of other pupils present were affected by the substance, as was a teacher who attempted to break up the fight.
"The youth is still being questioned and no decision has been made on what further action needs to be taken."
