Using one cohort of 7235 middle school students in Beijing, China, we examined the evolution of the gender achievement gap in middle school. Our study found a more significant female dominance than in U.S. studies: even though boys gradually caught up during middle school, especially in Math and Science, and the gender achievement gap decreased over the distribution of test scores, girls outperformed boys throughout primary and middle school and in each quartile of the performance distribution. As well, girls had a more positive school experience than boys, and boys had a higher dropout rate by the end of middle school. Despite significant gender differences in various important characteristics that have explained the gender achievement gap in the U.S., in our study, primary school test scores seemed to be the only significant source of the gender achievement gap at the end of middle school, indicating the importance of early intervention. (Contains 3 figures and 5 tables.)