I've discovered that students in Japan don't have the ability to properly structure their thoughts in a written essay. Each class that I've taught has always had to include how to structure an essay. This usually means an overall look at essays, but with class sessions devoted to constructing effective introductions, conclusions, paragraph structure, etc. You may run into the same problem in Korea.
I haven't taught students specifically for the SAT, but it would make sense to take a look at one of the prep books teenagers use for this part of the test. I'm sure that there are examples of essays, as well as key information on writing. You might also want to consider using essays written by teenagers. Not too long ago, I thumbed through a book of essays for college entrance requirements. Your students may find these interesting, as they have been written by their American peers.
Just a few thoughts. Let me know how the course goes!
Heads Up English - Materials based on current events. Just print, and teach!