Protesters gathered outside Hoërskool Akasia in Pretoria on Wednesday morning to demand placements for their children.
Police spokesperson Captain Kay Makhubele said around 50 protesters were there.
"Police are deployed to monitor the situation," he added.
Gauteng education department spokesperson Steve Mabona said there were "a few parents who blocked the … school entrances and demanded placement".
"The police were called to defuse the situation and learners and staff members were subsequently allowed access into the school. Accordingly, parents' representatives and members of the EFF met with the principal and school governing body," Mabona said.
The school has reached capacity but has undertaken to check if additional pupils can be accommodated.
"However, it must be indicated that they have already, in January 2021, introduced a new Grade 8 class to assist to manage the capacity challenge experienced in the area," Mabona added.
"The situation is calm and we wish to call upon members of the community not to disrupt schools."