About 50 hooded protesters held a demonstration at the San Pedro Nolasco School in Valparaiso on Monday, forcing the suspension of the University Selection Test (PSU), an annual national exam for entering higher education.
Footage shows groups of protesters confronting police, and police using water cannon to disperse the protest.
Reports in local media say the group of protesters threw tests into the street and engaged in several clashes with some opposing protesters. Some tests had already been completed by the students.
According to the state agency in charge of the PSU, the exam process was suspended in 64 out of the 729 schools taking part nationwide.
Police reported the arrest of 81 people for disorder, damages, and non-violent usurpation.