The National Teachers Union (Natu) has called on the provincial department of education to act decisively on claims that certain teachers at the troubled Ubuhlebomzinyathi School in Newcastle are using pupils to get rid of the principal.
Violence erupted at the school on Tuesday and learners stoned teachers and education officials to protest the reinstatement of the principal, whom they accuse of practicing witchcraft.
Natu vice-president Allen Thompson said provincial education officials were responsible for the current situation since they had failed to "reveal the findings of an investigation on the issue of bad blood between the principal and learners".
The department must take action against teachers who were implicated, Thompson said.
The decision to re- instate principal Nokuthula Gloria Madlala was taken by department officials and the school governing body last week.
Madlala had been off work since 2006.
On Tuesday officials escorted her back to school but angry pupils stoned vehicles, injuring four officials. The school is now closed.
Provincial head of department Cassius Lubisi has arranged for Grade 12 pupils to write exams at another venue.
"All exams for other grades are cancelled," Lubisi said.