Although gender differences in mathematics are smaller than they have been in the past, prominent voices still attribute these differences to a variety of fixed individual factors, such as genetic characteristics of men and women. We hold the alternative view that these differences can be ultimately attributed to malleable factors. From this vantage, societies could influence gender differences in mathematics by changing students' experiences in school. In this study, we built on prior work suggesting that mathematics anxiety causes lower mathematics scores. In particular, we found that mathematics anxiety entirely explains the gender differences evident in mathematics scores from the 2012 US Programme for International Student Assessment (PISA). Furthermore, we found that gender moderates the mediating role of mathematics anxiety: math anxiety is more detrimental for male than for female students. Because math anxiety is a malleable individual characteristic, we conclude that gender differences reveal more about gendered societal experiences than they do about innate characteristics of men and women. [For the complete proceedings, see ED629884.]