Traditionally, one of the largest costs of child-rearing has been the time spent by the mother, A good measure of the alternative cost of this time is what the mother could earn if she held a paying job. Thus, the long-term rise in women’s earnings has increased the “price” of children, and at any given time the price is higher for better-educated women because they have higher potential earnings. Better-educated women tend to have fewer children, and, if husband’s schooling is held constant, the negative effect of wife’s education on fertility is even more pronounced,
In cross-sectional studies at a given point in time, fertility tends to be higher the higher the husband’s education (holding wife’s education constant) because of the positive relation between his education and family income. Over time, however, rising income also raises the “price” of children because expenditures per child are closely tied to the income and living standards of the parents. This rise in “price” may result in a decrease in the number of children demanded, even though total expenditures on children (number times expenditures per child) usually rise as income rises.