I almost choked on my Cheerios Wednesday morning when I read about an incomprehensibly sexist tee-shirt that JCPenney had attempted to market to tweener girls. The shirt not-s0-subtly trumpeted the retro stereotype that girls can be smart or they can be pretty.  But never both. Its slogan, emblazoned front and center in colorful girly writing, was this:  “I’m Too Pretty to Do Homework, So My Brother Has to Do it For Me.”

Color me outraged. The design, if you can call it that, featured hearts, flowers and a couple of easy math problems — one of them left undone.

The good news is that thanks to a fast and furious barrage from the twitterverse, JCPenney pulled the shirt off the market and, in fact, apologized. (As an aside, JCPenney has another tweener shirt still on the market.  This one pimps a girl’s best subjects as boys, shopping, music and dancing.)

But the bad news is that they ever came up with any of this backlash-y nonsense in the first place: As if the “too pretty to do homework”shirt itself weren’t enough to set girls back a generation or two, take a gander at the ad copy: “Who has time for homework when there’s a new Justin Bieber album out? She’ll love this tee that’s just as cute and sassy as she is.”

Cute?  Sassy?  Justin Beiber?

The mind boggles and the heart sinks. It doesn’t take a degree in psychology to recognize that when girls are told that they’re no good at something — or that there’s still this false dichotomy between beauty and brains — it often becomes self-fulfilling prophecy. And so we have to wonder: is this kind of messaging one reason why — as Slate writer Shankar Vedantam noted a few months back:

Less than one in five professors of science and math at top research universities in the United States is a woman. The gender distribution of engineers at top Silicon Valley companies is similar to the gender distribution of the audience at your average strip club.

Strip club? Ouch.

Obviously, it’s all a bit more complicated than the outdated message that there’s beauty or there’s brains, and never the twain shall meet. But you have to wonder if these kinds of messages, subtle or otherwise, that we send to little girls often set the stage for deeper obstacles that keep women out of the game when it comes to math and science. Slate’s Vedantam went on to cite a study by Amherst psychologists who found that college women did better in math and science — and felt more comfortable in their abilities — when their professors were also female.

You don’t have to be a science geek to know where this is headed: the subtle discrimination that often impacts our choices.  And part of that discrimination — let’s just call it sexism — may have to do with whether or not we have role modes who look like us and who make us feel that we belong.

An earlier study likewise suggested that women avoid math and science, not because they lack the aptitude, but because they don’t feel welcome. Call it identity threat: women may avoid situations — like math or engineering — when they feel outnumbered. Researchers Mary Murphy, Claude Steele and James Gross found that when women math, science and engineering undergrads simply watched a video that pitched a fictional conference where men outnumbered women, the women showed the physical signs of threat — faster heart rates and sweating — and reported a lower sense of belonging, and less desire to participate in the conference at all. The researchers also found that the women who watched the gender unbalanced video were more vigilant of their surroundings overall.

The point? Sometimes it’s the threat, as much as the reality, that does us in. Which could be why we often end up side-stepping opportunities instead of marching right in, loaded for bear. It’s kind of a chicken-or-egg scenario:  Women who want to succeed — in math, science or the corporate boardroom — are more likely to do so if there are other women before them to pave the way. But how do those women get there?

Back to JCPenney and their sexist tee-shirt, the first step may be making sure young girls know that they don’t have to chose between beauty and brains — or Justin Beiber and schoolwork.  And that, when it comes to their homework, they can do as well as their brothers any day.

Even when it’s math.