Wednesday, July 24, 2013
By now, many of you have probably heard or read about the new study on social mobility, which is said to be the most comprehenisve study of it kind to date in the United States. The headline of most stories is the role that zipcodes play in social mobility. In short, where a child grows up will have a significant impact on his or her ability to climb out of poverty or stay in the middle class. The more important question, however, is why geography matters. The research examined various factors in the attempt to isolate the differing mobility rates and found that:
Although tax policies may account for some of the variation in outcomes across areas, much variation remained to be explained. . . . [W]e found significant correlations between intergenerational mobility and income inequality, economic and racial residential segregation, measures of K-12 school quality (such as test scores and high school dropout rates), social capital indices, and measures of family structure (such as the . . . fraction of single parents in an area). In particular, areas with a smaller middle class had lower rates of upward mobility. In contrast, a high concentration of income in the top 1% was not highly correlated with mobility patterns. Areas in which low income individuals were residentially segregated from middle income individuals were also particularly likely to have low rates of upward mobility. The quality of the K-12 school system also appears to be correlated with mobility: areas with higher test scores (controlling for income levels), lower dropout rates, and higher spending per student in schools had higher rates of upward mobility. Finally, some of the strongest predictors of upward mobility are correlates of social capital and family structure. For instance, high upward mobility areas tended to have higher fractions of religious individuals and fewer children raised by single parents. Each of these correlations remained strong even after controlling for measures of tax expenditures. Likewise, local tax policies remain correlated with mobility after controlling for these other factors.
A New York Times story reported that "Lawrence Katz, a labor economist who did not work on the project, said he was struck by the fact that areas with high levels of income mobility were also those that established high school earliest and have long had strong school systems."
If I read the study's underlying data correctly, the local high school dropout rate has three times the effect on social mobility as does tax policy, and local achievement test scores have two and a half times the effect on social mobility. Although not as heavily reported, the level of local segregation also had a significant impact on mobility. But to be clear, the data showed family structure (divorce rate, single parents, and teen mothers) to have the largest impact on social mobility, though only slightly higher than the drop out rate.
My only quibble with the study is its labels. According to the study's authors, chivement test scores and drop out rates are proxies for school quality. As school finance litigation and educational social science have demonstrated, those factors are relevant but school quality cannot be reduced to them. High achievement test scores are also largely a function of underlying student demographics and segregation. It is not clear to me how the current study controlled for this. If it didn't control for it, then achievement test scores alone don't really signify school quality. If it did control for underlying factors, then the study may have a point.
I am more inclined to recognize drop out rates as having more singular importance (even though the same issues of underlying demographics are relevant). After all, if a school cannot keep its students enrolled and graduate them, I believe the school is not doing all that it should. A better school would do more. With that said, high school drop out rates speak more directly to the need for drop out prevention programs than general school improvement programs. So again, I would hesitate to treat drop out rates as a general measure of school quality.
Regardless, the bottom line still seems to be that schools matter. They are the most important public lever we have for creating opportunity. And other policies, like taxes, look like red herrings. They certainly can ease the pain on struggling families, but they are insufficient to fundamentally change children's futures.