According to the North Gyeongsang Provincial Police Agency, a senior student, surnamed Kim, 18, from Dogye high school in Gumi, twice kicked a female teacher in the ribs for scolding him.
Kim was immediately suspended. The teacher is being treated in hospital.
The teacher said she had ordered Kim to settle down after the bell rang to start class.
A disciplinary committee will meet next week to determine Kim’s punishment.
Police said the teacher had no plans for now to take action against the student.
The North Gyeongsang Province education office and the school have been criticized for refusing to comment to the media about the incident.
Police plan to summon school officials and Kim’s classmates as part of their investigation.