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Take a photo of the class and write their names above their heads. Really, it's the obvious answer!
I have found, working at an all Girl's high school for the past two years, trying to learn their names earns you respect from the students. I wish we, Native English Teachers, didn't have to teach so many students, but this is the job we are signed up for. I try to learn something about some of the students or i just give them nicknames really. I have found the students have been using some of the nicknames that I gave certain students. I think one or two of them even like their nickname more than their real name. But, I would go with a seating chart and have the Korean teacher help you with the seating chart or at least getting the names of all of the students in each class so that you can do it yourself. Good Luck