Have you ever heard a girl say she hates math because she's "no good" at it? I've heard it plenty of times, even from my own daughter who actually has an aptitude for the subject.

Research has shown that children believe their ability to do certain things depends on how much natural ability they have for the task. These so-called "entity theories" can affect their performance.

And now a recent study from the University of Illinois at Urbana-Champaign that involved 4- to 7-year-olds suggests that children can adopt these beliefs from information they hear about their gender or certain social groups.

According to the study, published in Psychological Science, researchers had "hypothesized that the mere act of linking success at an unfamiliar, challenging activity to a social group gives rise to entity beliefs that are so powerful as to interfere with children's ability to perform the activity."

Conducting two experiments involving 144 kids, the researchers found that the children's performance was "impaired by exposure to information that associated success in the task at hand with membership in a certain social group...regardless of whether the children themselves belonged to that group."

So that means that if a girl hears that girls are supposed to be bad at math, she may believe the same about herself and therefore do worse than she should, says a story on the online magazineSlate that also suggests the research may explain why there's a persistent gender gap between boys and girls when it comes to pursuing careers in math and science.

The lesson for parents and educators? Make sure we teach kids that they all have the opportunity to be "good" at something if they put in the effort.