Sorry, boys, but the news only gets worse.

Across the board, data show that women are better students than men. From test scores to college graduation rates, females outperform males in almost every metric of educational achievement.

Now, two economists from Texas A&M University report that schoolgirls do even better than their male counterparts when they are taught by female teachers. Specifically, the authors found a significant change in female test scores in math—long considered the last bastion of male educational dominance—when taught by a woman instead of a man.

Jonathan Meer and Jaegeum Lim analyzed the standardized test scores of over 14,000 middle school students in South Korea and found that when taught by a woman, girls’ scores on average were almost 10% of a standard deviation higher than boys. The economists also found that when switching from a male to female math teacher, girls’ scores rose by 8.5% of a standard deviation compared to the boys’ scores.

“Female students outperform male students by roughly a third of a school year more when taught by female teachers than when taught by male teachers,” Meer explained to Quartz by email (emphasis in the original.) They arrived at that estimate by using the findings of a previous study, which argued that a 1% difference in standard deviation on test scores corresponds to around 10 days of schooling.

Meer thinks the change in performance for female students may be due to their comfort levels in the classroom when being taught by someone of the same gender. “Female students report feeling that their female teachers are more likely to give students an equal chance to participate,” he writes, adding that “their female teachers are more likely to encourage creative expression.”

This may be great news for young women learners, but Meer believes these findings are worrisome for anyone concerned that boys are increasingly falling behind their female classmates in school. ”I’m personally deeply worried about male performance in schools,” Meer wrote, citing the mounting evidence showing a large and growing gap in educational achievement between females and males.

Meer and Lim used South Korea for their natural experiment because the country mandates that students be assigned at random to classrooms. Nonetheless, the economists made sure to confirm that these assignments were truly random, unlike in the US where evidence points to female math teachers frequently being assigned to classes with weaker students.

Teaching, of course, remains a heavily gendered profession, with women far more likely to enter the field than men. In their study, Lim reports that 68% Korean language, 73% of English language, and 61% of math teachers were women.

This gender imbalance may steer men away from the profession. This could theoretically impact the quality of male teachers, which, in turn, could be the source of why female students do better when taught by more qualified, female teachers. But if this were true, male students would also experience a similar rise in test scores when taught by a woman, of which Meer and Lim found no evidence.