This chart from David Wessel looks like encouraging news at first glance. For decades, U.S. high-school graduation rates have been stagnating. But according to a new paper from Harvard's Richard Murnane, graduation rates have climbed rapidly since 2000:
But here's the kicker. No one seems to know why graduation rates suddenly started spiking for men and women born after 1976. Even the researchers themselves are befuddled:
Mr. Murnane says he and other academics can’t fully explain the fall and rise of high school graduation rates. The economic reward for getting a diploma — higher wages — is substantial and grew during the years when dropout rates were rising, confounding economists who would have expected that to encourage people to finish high school.
The economist, a professor at Harvard’s education school, speculates that some high school students dropped out when high schools raised standards for graduation because they realized they wouldn’t get over the bar.
The recent improvement, he speculates, may be the welcome byproduct of a upturn in math and reading skills, as measured by test scores, among minorities in the years before the students reach ninth grade. Alternatively, Ms. Goldin suggests, the lousy economy of the late 2000’s may have led students to stay in school because jobs were so scarce.
Karl Smith mentions another possibility no one is considering: lead. Recently, Kevin Drum has gone on a tear about how the drop in lead pollution during the 1960s and 1970s may have driven the subsequent decline in U.S. crime rates. (Plenty of evidence suggests that lead does terrible things to our brains.) Perhaps the reduction in lead also accounts for the improvement in graduation rates. Just a theory, but no one seems to have a better one.
Why is it so crucial to know what the cause is? In part because many policymakers and states would like to see those graduation rates keep improving. Drop-out rates are still quite high, after all. Nowadays, one-fifth of all men and one-seventh of all women between the 20 and 24 lack a high-school diploma, which in turn makes it harder for them to get decent-paying jobs.
In his 70-page paper (pdf), Murnane notes that researchers still aren't quite sure how to boost graduation rates. The modest policy reforms that are easy to study — such as randomly assigning certain ninth-graders to literacy programs — don't appear to be very effective. Big, ambitious interventions that revamp entire schools seem to be more promising — such as the push that Brockton High School in Massachusetts made in the 1990s to reduce its drop-out rate. The catch is that those programs are also harder for economists to evaluate.