Exhibit number one billion in the case of Stupid People v. Yes, Sexism Is Still a Thing: turns out, no matter how good girls are at math, teachers still might be biased against them in the classroom. Data from a national 2002 study indicates that a small but significant percentage of teachers believe that math is just easier for boys than it is for girls (girls KILL IT in shopping class, though!).

Via msnbc:

Teachers tend to rate white girls' math abilities lower than those of white male students, even when the girls' grades and test scores are comparable to boys, according to a team of researchers who analyzed data collected as part of the national Educational Longitudinal Study of 2002.

"We find evidence of a consistent bias against white females, which although relatively small in magnitude, suggests that teachers hold the belief that math is just easier for white males than it is for white females," write Catherine Riegle-Crumb and Melissa Humphries of the University of Texas at Austin in the April issue of the journal Gender & Society.

This is the kind of thing we're talking about when we talk about institutionalized sexism. That bias is probably so ingrained that the teachers themselves don't even notice it's there, but an invisible bias can still cause visible problems for vulnerable girls. Sure, teachers aren't literally sending the girls out to try on wigs during math class, but it's discouraging to feel—however subtly—that your mentor doesn't have confidence in your abilities or expectations for your success. We're getting into dangerous self-fulfilling prophecy territory here. Hooray! As if self-perpetuating math anxiety wasn't enough.