alt Hacker NewsI used to TA a graduate level CS math class at Georgia Tech. We regularly saw that the students who self-organized study groups did dramatically better in the course than average. One semester they told us to put everyone in study groups to see if it helped. The effect disappeared. Turns out that it was the self-selection of the most engaged students into a small group that mattered, not the study group itself.
So there might be zero effect?
If it's purely a correlation, then maybe those students would be more successful than average even without the study group. They're already the most motivated kids. Maybe they just do "motivated kid stuff" and would still outperform.