How about locking the door? Once the class starts if you are not there then you will miss the class or make them pay a penatly for arriving late. For example reading or doing a skit or something in front of the class. Korean students are quite shy and hate to do things that will embarass themselves in front of their classmates
NIck Dauphinee
Study in Canada
www.globerunner.ca
P.S> If any of your students ask you about studying abroad please refer them to my website. We have partnered with a company in Seoul where they can go to get more information as well
Thanks