Open AccessFor most of the 20th century, American women had, on average, lower educational attainment than men. Researchers often theorize that differential treatment by parents based on children’s genders played a role in this result, but they rarely examine directly whether siblings from the same family were unequally affected. This paper redresses this lacuna by asking two questions: (1) Is the gender gap in educational attainment in the population at large as evident within families? (2) Does parental socioeconomic status (SES) attenuate or exacerbate education differences between sons and daughters? Using the Study of American Families, fixed effects regressions initially suggest that families did favor sons over daughters, but upon closer examination, only high SES families generated higher-educated sons than daughters; low SES families produced equally-educated sons and daughters. These results are contrary to the predictions of gender egalitarianism theory. Additionally, this paper uncovers that if a father had more education than his wife, their son was more likely to surpass his sister educationally, net of family SES; this highlights the reproduction of gendered relations of educational advantage across generations.