Kids need a crap load of sleep and they are going to get it one way or another. As I mention in the next post, kids sleep in class here. One major cause of sleepy kids is they sleep 48 minutes less per night than kids in the US according to this story. The main reason: kids spend an average of 2 hours and 6 minutes a day in cram schools. So some of the effects of the cram schools are offset by sleeping in class.
I also wonder about how diet affects the kids. Koreans, at 3.5%, have the lowest rate of obesity in the OECD according to this article. Lower than even the Japanese. I do not know if diet plays into the sleepiness equation, but I know that for the first three months I was here I was exhausted every afternoon and had to sleep. Finally, I changed my breakfast and saw a dramatic improvement in my energy level.