dr. christina kwasnica, dr. alexander dromerick, we thank you both for helping us understand it all better. thank you. >> brown: next, making the grade where the pressure is on. margaret warner reports from south korea. >> warner: just outside seoul, high school freshman yoo jae won gets ready to study. his mom and dad, both doctors, already out the door; big sister, away at school. so that means all the more time to spend with the lovely miss lee. jae won's virtual teacher leaves this 16-year-old with virtually no time off, and that's the way he wants it. >> i think i need to study and work harder for my future. >> warner: that's a widespread belief in south korea, where extraordinary passion for education is the norm. have we mentioned jae won is on his two-month winter holiday? no matter. he began his day by walking in the biting cold, past a billboard touting perfect- scoring students, to a 90-minute math tutoring session and study hall. the tutoring was at a private cram school, or hagwon. from early mornin