Tensions are escalating between the police and protesters outside Hoërskool Overvaal in Vereeniging.
Police tried to disperse protesters with rubber bullets and tear gas.
Protests began outside the school last week, with marchers calling for transformation and a change in the school's language policy.
The protests were sparked by a High Court ruling which found that the school didn't have capacity to accommodate 55 English speaking pupils.
The South African Council of Churches said earlier the school needed to be protected to ensure that children were able to attend classes.
The council said that transformation in South Africa could not be stopped and consensus would be reached if all the relevant leaders met to talk.
A delegation from the council is visiting the school on Monday.
The council's Gauteng secretary-general Reverend Gift Moerane said: “And therefore we say, even court cases are not going to help this country for transformation. But its only when leaders sit around the table and talk and we present our issues on the table.”