The incident caused panic in the Community Secondary School, Oroworukwo, prompting several students who were scared to start jumping down from the first floor of the two-storey of the secondary school.
The SS2 student had got to school with the canister on Thursday and while he and others were fiddling with it, it exploded, the Rivers State Police Command said.
According to the Guardian news website, It was alleged that SS 3 and SS 2 students of Community Secondary School had intended to clash that fateful day the tear gas exploded.
The student is said to have brought the tear gas to school as part of the SS2 students arsenal.
Some casualties with fractured hands, legs, injuries and asthmatic patients were recorded and are now in the hospital.
The student told the police that he picked the canister from the residence of his late uncle who was a police officer.
He has been granted bail, the police said, pending further investigations.