I coulda told you that.

According to this article on english.chosun.com, Korean kids don't get enough sleep. The final paragraph is of special interest:

The research team said, "We found that the more hours the children spend at private cramming institutes, the less satisfied they and their parents are with their performance; and the more obese the children are, the fewer hours they sleep." "Special attention is needed, because sleep deprivation has negative effects such as diseases, psychological instability, poor performance, and stunted growth," it warned.