AbstractUS women, on average, had approximately two children in both the 1930s and in the 1970s, yet the fertility distribution in the 1930s was less concentrated. This implies change in reproductive behavior, which cannot be captured by models focusing on average fertility. To explain these changes, I have developed a model that makes a distinction between sons and daughters. In this model, the female labor force participation rate is the probability of each girl becoming an employed woman. This endogenizes the empirically observed difference in the propensity for an all-girl household to have another child compared to an all-boy household, generating large fertility differentials at low participation rates. Higher participation rates raise the expected return from an additional child, as well as the expected return from existing daughters. The first effect tends to increase fertility, while the second effect, for relatively concave utility functions, tends to decrease it, so that the distribution of completed fertilities becomes more concentrated.