A 17-year-old pupil was arrested at KwaMbonambi in Mtubatuba, northern Zululand, after he allegedly pointed a loaded gun at his classmate in front of other pupils.
Police spokesman Captain Jabulani Mdletshe said the Dlemudlemu High School pupil was arrested on Monday.
"The police were called in and they found the boy had a gun (a Z.26 model) loaded with bullets," Mdletshe said.
"At this stage, police are still investigating how he got hold of the gun and whether it's a licensed firearm or not.
"But one thing the pupil indicated was that it was a family firearm, but he could not tell why he brought it to school."
The incident happened barely a week after a Grade 8 pupil at Zamazulu High School, Sphamandla Dlamini, 15, was shot dead in a classroom by another 15-year-old after wrestling for the possession of a firearm.