A secondary school teacher in northern Greece has been arrested after being accused of gagging a 13-year-old student during class and instructing another pupil to restrain him, an incident that has sparked widespread outrage.

The alleged incident took place at a junior high school in the city of Serres, where a 60-year-old teacher — who also serves as the school’s principal — is accused of taping the student’s mouth shut with insulating tape during a lesson, reportedly as punishment for causing a disturbance in the classroom.

According to a complaint filed by the boy’s mother with the Serres police on Friday, the teacher allegedly escalated the incident by ordering another 13-year-old student to tie the boy’s hands using paper tape.

Greek public broadcaster ERT reported that the incident occurred during the first teaching period of the day. Parents were later informed of what had taken place and moved swiftly to report the matter to authorities.

The teacher was arrested by police and on Saturday was brought before a public prosecutor. An investigation into the incident is ongoing.