The National Office of Investigation (NOI) under the Korean National Police Agency said it has probed 69 people and referred 24 of them to the prosecution in connection with inquiries into the collusive "cartel" relationships between public and private education sectors.
All of those referred to the prosecution were incumbent high school teachers working in Seoul.
They allegedly received between 100,000 won (US$72) and 300,000 won per question, Korea Times reported.
The NOI said it sent 24 teachers to the prosecution without detention on charges of violating the anti-graft law and obstructing hierarchical justice.
According to the police, 14 teachers allegedly created and provided private questions to large entrance exam academies from April 2019 to November last year.
Among them, one was found to have collected 254 million won in return, Maeil Business Newspaper reported.
The teacher is alleged to have participated in a review panel for a state-administered practice test last year, and is accused of using insights from that session to create 11 questions which he then sold to two private institutions.
He refuted the accusations, claiming there was no link between the practice test and the questions he sold, but police confirmed their similarity following expert assessments.