Sex ratios, i.e., relative numbers of men and women, can affect marriage prospects, labor force participation, and other social and economic variables. But the observed association between sex ratios and social and economic conditions may be confounded by omitted variables and reverse causality. This paper uses variation in immigrant flows as a natural experiment to study the effect of sex ratios on the children and grandchildren of immigrants. The flow of immigrants affected the second generation marriage market because second generation marriages were mostly endogamous, i.e., to members of the same ethnic group. The empirical results suggest that high sex ratios had a large positive effect on the likelihood of female marriage, and a large negative effect on female labor force participation. Perhaps surprisingly, the marriage rates of second generation men appear to be a slightly increasing function of immigrant sex ratios. Higher sex ratios also appear to have raised male earnings and the incomes of parents with young children. The empirical results are broadly consistent with theories where higher sex ratios increase female bargaining power in the marriage market.

The twelfth century rabbinic scholar Maimonides proposed a maximum class size of 40. This same maximum induces a nonlinear and nonmonotonic relationship between grade enrollment and class size in Israeli public schools today. Maimonides' rule of 40 is used here to construct instrumental variables estimates of effects of class size on test scores. The resulting identification strategy can be viewed as an application of Donald Campbell's regression-discontinuity design to the class-size question. The estimates show that reducing class size induces a significant and substantial increase in test scores for fourth and fifth graders, although not for third graders.

We use student assignment lotteries to estimate the effect of charter school attendance on student achievement in Boston. We also evaluate a related alternative, Boston's pilot schools. Pilot schools have some of the independence of charter schools but are in the Boston Public School district and are covered by some collective bargaining provisions. Lottery estimates show large and significant score gains for charter students in middle and high school. In contrast, lottery estimates for pilot school students are mostly small and insignificant, with some significant negative effects. Charter schools with binding assignment lotteries appear to generate larger gains than other charters.