And the usually unstated observation is that Finnish and most other European school systems have a much stronger tracking mechanism than U.S. schools--not in the sense of "knowing where the kids are," but in the sense of putting them into classes oriented towards universities or not, trade school or not, and such. As a result, kids at the lowest rungs aren't necessarily taking the tests if they've already left or enter vocational education, and the ones at the bottom aren't holding back the ones at the top.

That is just wrong regarding Finland. The WSJ article linked in the grandparent post specifies 15-year old students at excelling at international tests. In Finland that is 9th grade or final year of middle school. The first "tracking" happens after the 9th grade with the students enrolling in either "lukio" high schools or vocational schools. Up to the 9th grade there is little to none tracking of students based on their abilities. My personal opinion is that there should be somewhat more tracking. The current system allows the gifted students to cruise and does not challenge them because most of the teachers' effort will be in the low end of the bell curve.

disclaimer: I am a product of the Finnish educational system and my direct experience with it is about a decade old.