Neat article Herrick. My guess is that the residual genetic drivers of school achievement relate to personality.

For example, conscientiousness, related to hard work and dedication to achievement, stability (the converse of neuroticism) related to the lack of test-taking anxiety and calmness under time pressure, and perhaps introversion, because extraverts tend to spend less time studying than they do socializing. These things have been found in some studies I've read on the link between personality and school grades. Oh, and possibly agreeableness as well since teachers rate children higher who play nice with the other kids and act politely.

I imagine extroversion correlates negatively with school achievement and positively with income.