I have blogged earlier about the significant positive co-relationship between parental care, peer effects, and societal environment on the one hand and educational outcomes on the other. Economix enriches this literature by comparing this year's SAT scores in the US with student family incomes and finding very strong positive co-relation between the two - higher family incomes co-relate with higher test scores. It finds that on every test section, moving up an income category was associated with an average score boost of over 12 points.
The conclusion is not that higher incomes causes higher test scores. But, that students from families with higher incomes stand a substantially greater chance of getting higher test scores, for a variety of reasons. In other words, their economic backgrounds confer a disproportionately high advantage on the children from well-off families.
Now, there is nothing profound about this conclusion. Its theoretical foundations have been superbly illuminated by the late John Rawls in his second principle of justice (the difference principle) - those with comparable talents and motivation should face roughly similar life chances, and that inequalities in society should always work to the benefit of the least advantaged. But it is unfortunate that this does not get reflected, in as unqualified a manner as it should, in public debates on social issues and when public policies are designed.
Greg Mankiw points to an omitted variable bias and claims that the positive co-relation is due to the fact that "smart parents make more money and pass those good genes on to their offspring". Paul Krugman responds by pointing to this which shows that "students with low test scores from high-income families are slightly more likely to finish college than students with high test scores from low-income families".