[throwaway4891a]

Also, middle-/upper-oriented people are more likely peer-pressured to placing in the "best" kindergartens, whereas lower-oriented people may skip it (much like skipping parental-school involvement). And, I suspect both nature and nurture aspects are self-amplifying: smarter/more competitive kids may make more money and attempt to seek similar mates to have improved offspring and try really hard to inculcate successful attitudes. Plus, having more money helps reinforce getting into selective kindergartens and making more childhood friends of future powerful people, leading to better social access to higher quality mates (better genes), more money and hopefully better lifestyle-choices.

[jannotti]

Right, I'd really like to know about the "random" process that assigned students to classrooms. I know that when I was in elementary school the assignments were theoretically random, but if parents really wanted to influence them, they could. Since this study gets a lot of its results from clustering, they might just be finding that certain classes were perceived to be better (right or wrong) and so involved parents influenced the school to get their kids in it. Now it really is going to be "better" by the metric of those kids' later success.