How much does education matter?

Greg Mankiw thinks that correlating SATS scores and subsequent earned income misses the point that inherited intelligence are a factor in both. This appears to be supported by the graph in Alex Tabarrok's blog that shows "higher parental income predicts higher child income but only for biological children and not for adoptees."

David Davis points out that the £45,000 true cost of a university education is not always recouped by graduate earnings. (See also Charles Hugh Smith's piece, "Is Higher Education Worth a Lifetime of Debt?")

I have read that there is a positive correlation between shoe size and IQ. Public policy is to buy big shoes for everybody so they get smarter.