Princeton University and NBER
Discussions of cross-sectional fertility heterogeneity and its interaction with economic growth typically assume that the poor have more children than the rich. Micro-data from 48 developing countries [e.g., Mexico, Bangladesh, Indonesia] suggest that this phenomenon is very recent. Over the second half of the twentieth century, these countries saw the association of economic status with fertility and the association of the number of siblings with their education ?ip from generally positive to generally negative. Because large families switched from investing in more education to investing in less, heterogeneity in fertility across families initially increased but now largely decreases average educational attainment. While changes in GDP per capita, women’s work, sectoral composition, urbanization, and population health do not explain the reversal, roughly half of it can be attributed to the rising aggregate education levels of the parent generation. The results are most consistent with theories of the fertility transition based on changing preferences over the quality and quantity of children, and somewhat less so with theories that incorporate subsistence consumption constraints.
Basically, in quasi-Malthusians societies, well-off people had more surviving children, as Greg Clark demonstrated for England in A Farewell to Alms. Typically, rich people got married younger. Francis Galton noticed that the relationship was flipping toward the opposite direction in modernizing England. Vogl's studied shows the same process has happened for the Third World, just much more recently.
Of the three countries he has the most data for, Mexico, Bangladesh, and India, Mexico had a tiny positive relationship between education and fertility in the 1940s, but it was quite negative by the 1970s. Uh oh ...