Around the globe, educational opportunities and outcomes have long varied in relation to student gender. Within the United States, a particularly intense and growing controversy concerns whether education should be delivered in single-sex contexts. This paper offers a broad framework for approaching this controversy. I review arguments made by historical and contemporary proponents of genderdifferentiated education, concluding that these reveal a foundational commitment to gender essentialism (rather than to gender constructivism more commonly embraced by critics of single-sex schooling). I suggest that different gender conceptualizations and different professional traditions affect the kind of data one collects, weighs, and reports. Gender conceptualizations also affect the valence assigned to the amplification or attenuation of gender differences in educational, career, or personal student outcomes. I then propose that other kinds of human values are also relevant to the controversy. Given that in justifying their position, advocates of single-sex public education have recently been focusing less on gendered brain differences and more on the expansion of educational choice, I focus especially on the value of choice. Using arguments paralleling those found in critiques of the U.S. charter-school movement, I suggest that decisions about school choice necessarily entail judgments about a range of goals and human priorities. I close by suggesting that a resolution of the controversy about single-sex education cannot be reached through empirical data alone, but will require discussions of gender conceptualizations, what constitutes evidence, ideal educational outcomes, and broader human values.