Lethbridge police say three boys got into a fight outside Chinook High School during the lunch hour Wednesday.
Police allege one of them, a 15-year old who is not a student at the school, was hit by the two other teens.
Police say the 15-year-old then discharged a can of pepper spray at a crowd of about 20 students who had gathered.
The teen is to appear in youth court next week on charges of assault with a weapon and possession of an offensive weapon dangerous to the public.
Police say assault charges are pending against the two other boys involved in the fight.