@greenmoriyama
The reason I posted is because I don't understand the Japanese system, not because I do. But I do understand the American system. I've worked in education, at American high schools (in addition to of course my own studies, and tutoring high school and college age students).
I do as well understand that the Japanese basically are willing to let kids stop going to school at 14/15 and just enter the workforce with a middle school education. That's something Americans don't do though - you have to be 16 to drop out here, and your employment prospects will be close to nil without a diploma.
So basically with Americans, every year builds on the previous year's knowledge. Understanding 70%+ of the material means you have a pretty decent understanding of it. That's crucial to have, because your next class in that subject is going to assume first that you already have that previous knowledge and will apply more advanced concepts.
If a student were only absorbing 30% of the knowledge of like, 6th grade math, there's no way he or she would be prepared for 7th grade math. They'd just start falling further and further behind -- which is why American schools won't let a student move on until they've mastered the current concepts -- there's literally no point in taking the next class, because they don't have the tools to succeed yet.
American schools are certainly guilty of just passing kids without actually teaching them. It happens all over. For example, in Detroit only 1 in 20 students can read and do math 'at grade level proficiency'. Meaning like, 1 in 20 students would be getting a 60-70% or above and 19 out of 20 would fail. Another story that recently hit the news is that a teacher was fired because she gave a student a zero for projects not turned in -- and apparently the school's policy is that the lowest score a student can receive is 50% on any assignment. (which is total bullshit and not normal btw). But yeah so in that school, all scores would be between 50% and 100%.
As far as my personal education, I didn't do much in the way of advanced courses. I went to a small, rural school. The only 'advanced' course I took was I skipped 7th grade math and started with 8th grade math, so I was 1 year ahead. Otherwise, my education in school was the same as every other students'. I just read a lot on my own for fun. In fact I slept through most classes my senior year, and stayed up all night just playing video games
As far as my personal college experience, I never once had a class where we were tested on materials not covered in class. Like there would be assigned readings, but we would eventually talk about/discuss those readings, and there would be lecture notes to take, but every single class I ever had, the teacher would explain exactly what material was going to be covered on the test. It was up to us to do the studying necessary, but we at least knew like, "You'll be tested in multiple choice about concepts from pages 1 through 216 in Book X, and pages 75-153 in Book Y. Here's a list of 30 possible essay questions. There will be four questions from this list on the test."