Gina Kolata of the New York Times discusses research showing that staying in school longer tends to extend life. A key paper is by Adriana Lleras-Muney. Her approach to sorting out causality and confounding effects:
between 1915 and 1939, at least 30 states changed their compulsory schooling laws and child labor laws. If compulsory schooling laws forced people to get more schooling than they would have chosen otherwise, and if education increases health, then individuals who spent their teens in states that required them to go to school for more years should be relatively healthier and live longer.
Suppose that a law was passed in a given state saying that all children born after January 1, 1925 had to attend school through 10th grade, where previously they only had to attend through 6th grade. Then, if we observe a discontinuity in the longevity of people born after January 1, 1925 compared to people born just before, this is plausibly due to greater schooling. Greg Mankiw rightly points out the value of such methodology.
I am inclined to a prior that the value of years of schooling tends to be overstated in general, which makes me a "motivated skeptic" of the Lleras-Muney result. But I am hard pressed to come up with an attack on her appoach.
Still, the quantitative effects are small. Kolata writes,
It turned out that life expectancy at age 35 was extended by as much as one and a half years simply by going to school for one extra year.
For someone who hates school, this might not be compelling. (If spending a year in prison increased your life expectancy by eighteen months, would that make you want to do time?)
To me, the main value of Kolata's piece is to point out that not all improvements in longevity and other health outcomes are due to medical treatment. This is an important fact to keep in mind.
UPDATE: For more on this topic, see this paper by David Cutler and Lleras-Muney.
Behavioral differences by education are large. Nearly 30 percent of people with less than a high school degree smoke, three times the rate of people with a college degree. Twenty-four percent of people with less than a high school degree are obese; twice the rate as college graduates. Eight percent of adults who have not completed high school are heavy drinkers, double the rate of college graduates. The impact of these three behaviors on overall differences in health is significant.