The incident took place outside Marklands Secondary School in Shallcross, south of Durban, in KwaZulu Natal, on Monday morning.
It is unclear exactly who fired the fatal shot.
One of the alleged hijackers is also reported to have died, apparently after they lost control of the car.
Hijacking is a major issue in South Africa. In 2016, an average of 1,416 vehicles were hijacked every month – equating to one every 32 minutes