In the late 1990s, it became apparent that there was a gender gap in math achievement among American students. A study performed in the 1998-1999 school year found that girls were falling behind in math as early as kindergarten, with the gap widening as they aged through the school system.

Problems like this were supposed to be addressed by programs like No Child Left Behind, but it turns out that the 2010-2011 cohort of kindergartners have the same problem, and at almost the exact same rates.

Girls are still lagging behind boys in math, and researchers are not sure why. One possible explanation, though, is that teacher expectations and perceptions are a factor. Teachers as a whole seem to think that girls aren’t as good as boys at mathematics.

Even comparing boys and girls with similar behavior and similar math scores, teachers seem to be reporting that the girls have lower math skills. As early as first grade, teachers were underrating girls’ math skills in both the 1998-99 and 2010-11 cohorts.

“The gender gap at the top of the math achievement distribution deserves special attention, as this is where future mathematicians, computer scientists, and other STEM professionals tend to reside—professions in which women remain underrepresented,” says Associate Professor Joseph Robinson Cimpian of NYU, the study’s lead author.

While researchers are still trying to understand how these gender gaps form and maintain themselves, studies have shown that perceptions of children’s academic performance can have a major impact on that performance. The perception that girls are bad at math is manifesting itself as girls falling behind in the subject, both because they are being underrated and because they are being told they aren’t good at it. Telling a student that they aren’t good at a subject is a self-fulfilling prophecy.

It’s already been far too long since this problem was discovered, and even 12 years later, it’s still not been addressed.

Do you notice a math gender gap in your classroom? Do you think teachers have lower expectations of girls’ performance in mathematics? How do you address those issues? Please share your thoughts in the comments.