This is a phenomena also encountered in European universities. I know for a fact that it occurs in Physics and Math, since our professors were in the habit of s

This is a phenomena also encountered in European universities. I know for a fact that it occurs in Physics and Math, since our professors were in the habit of showing us performance statistics.They even tend to adjust the grading accordingly. That is you get a B approximately at the first peak and fail if you are significantly behind the second peak. I don't think it nescessarily has to do with income / prior education.