Some schools prefer their teachers to have had at least 100 hours of TEFL certification, especially with a classroom component. https://koeelds.com/%EC%97%AC%EC%84%B1%EC%9D%84-%EC%9C%84%ED%95%9C-%EB%B0%A4%EC%95%8C%EB%B0%94-%EA%B5%AC%EC%9D%B8%EA%B5%AC%EC%A7%81-%EC%95%88%EC%A0%84%ED%95%98%EA%B3%A0-%EC%9C%A0%EC%9D%B5%ED%95%9C-%EC%84%A0%ED%83%9D/