I keep thinking about Bruce Sacerdote’s Korean adoption study.  I’ve read every twin and adoption paper I could find about parental influence on kids’ educational outcomes.  Sacerdote’s is the best of the bunch – the cleanest study, the clearest presentation, and the most comprehensive analysis.

You may recall that Sacerdote found small effects of maternal education and family size on how far kids get in school.  As I summarized before:

[E]very extra year of maternal education raises kids’ years of education
by .097 years – about a month.  Every additional child in the family
reduces kids’ years of education by .129 years – about a month and a

What about the probability a kid finishes college? 
Every year of maternal education raises it by 2.3%; each kid in the
family reduces it by 2.6%.

OK, but why does maternal education and family size matter, however slight the effect?  Many economists will be tempted to say that families with more education and fewer kids have more financial resources to invest in each child.

It is striking, then, that Sacerdote controls for both family income and income in the family’s zip code.  Neither of these income variables has a statistically significant effect on kids’ educational success.  In fact, the sign is wrong three times out of four.  Despite their best efforts, in short, it looks like rich families fail to give their kids’ an edge in school.  It doesn’t even look like richer parents’ residence in better school districts pays off. 

On reflection, income – both family and neighborhood – is the dog that didn’t bark.  It prompts us to ask, “Why would maternal education and small families matter after controlling for their purely financial effects?”  Maybe it really is parental attention; maybe it’s some kid of sub-cultural osmosis.  The big news, in my view, continues to be that these effects are small.  But why do you think they matter at all?