The school said the booms were up when the robbery occurred as it was pick-up time.
"This traumatic incident is being fully and urgently investigated and leads followed up. The safety and security of all on our campus is a top priority," it added.
Police spokesperson Capt Mavela Masondo said a woman had been waiting for her child at the school parking area when she was accosted.
"The victim parked her vehicle at parking to pick up her child and another vehicle parked next to her. The suspect got out of the vehicle and approached the victim, grabbed her car keys and removed them from the ignition, threatening her," said Masondo.
"Another suspect came and forcefully remove gold bracelets from the victim's arm and fled."
The suspects dropped the parent's car keys before fleeing.