Investigators seized documents and computer files from eight private institutes, or hagwon, this week, following suspicions that the schools leaked test questions from the U.S. Scholastic Aptitude Test (SAT) to students, prosecutors said.
Seoul Central Prosecutors' Office said the raid targeted private academies in Gangnam, southern Seoul, that provide SAT lessons to students whose families pay high tuition fees.
One of the eight was established by Jeffery Sohn, 42, a well-known instructor who was indicted in January 2012 for leaking SAT questions in 2007.
Sohn obtained a copy of the Jan. 27, 2007, SAT test taken in Thailand and uploaded the questions on a web community page, so that his students could prepare answers prior to taking the same test.
SAT tests are taken on the same day around the world, but Son took advantage of time differences to enable his students to cheat.
The Education Testing Service (ETS) in the U.S. that defines itself as a non-profit organization also conducts TOEFL and GRE tests. It canceled the scores of 900 Korean students following Son's activities.
ETS was unavailable for comment.