Pupils at Cape Town's Protea Heights Academy in Brackenfell had to be evacuated on Wednesday after a bomb scare.
The Western Cape education department said the police's bomb squad was called in.
"Rumours that a device had been found is false," said department spokesperson Bronagh Hammond.
"Thankfully, candidates that wrote the Economics paper this morning were not affected," she said.
Police said the threat was emailed to the school and pupils were evacuated.
No bomb was found.
Sergeant Noloyiso Rwexana said police are investigating.
Tensions ran high at another school in the vicinity earlier this week after violent clashes took place at nearby Brackenfell High School, when angry community members confronted protesting EFF members over an alleged exclusionary private matric party.