after classes let up, sung-do studies for hours in a school cubicle and takes his dinner in a school cafeteria. he'll sometimes go to a late night cram school known in korea as a hagwon, nocturnal schools for kids offering classes in science, math or any other subject that's covered on the big college exam. after-school instruction is very popular here, enrolling three-quarters of the nation's students. the average korean family spends roughly 20% of their income on private tutoring. back home, sung-do usually continues his studies well after midnight. >> it's true that study hours is horrible. i might enjoy the pain i cannot avoid. i'm trying my best to enjoy this environment and this age. >> the korean education system is at the heart of an extraordinary economic success story.