A persistent belief in American culture is that males both outperform and have a higher inherent aptitude for mathematics than females. Using data from two school districts in two different states in the United States, this study used longitudinal multilevel modeling to examine whether overall performance on standardized as well as classroom tests reveals a gender difference in mathematics performance. The results suggest that both male and female students demonstrated the same growth trend in mathematics performance (as measured by standardized test scores) over time, but females' mathematics grade-point average is significantly higher than males. These results are discussed in the context of present day standardized assessment in the United States that may motivate teachers to focus on higher expectations for mathematics performance regardless of gender, thus challenging cultural beliefs that stigmatize mathematics as masculine in the United States.