An extremely interesting piece from RadioLab (a public radio program and podcast) talking about the "Obama Effect". A researcher gave subjects a questionnaire before Obama gave his inauguration speech. He found that whites scored slightly higher than blacks. After the inauguration a second group was given the test, but they were first shown the speech. The results were that the disparity between whites and blacks completely vanished.
A similar study showed a slight difference in math scores between males and females. However, before administering the same test to new subjects, the researcher told the students 'while you may have heard men normally score higher on math tests compared to females, this particular test shows no gender differences.' All differences dissapeared.
One last example they gave--researchers brought in subjects and gave them a putting (as in golf) challenge. When they presented the experiment as a 'test of athletic intelligence', they found blacks did about four strokes worse than their white counterparts. But when they presented it as a test of their 'natural athletic ability', those scores were reversed. Whites scored 4 strokes worse than their black counterparts.
In other words we learn about stereotypes in life, and even if we don't believe them, we often end up 'fulfilling' those expectations. So the next time you think to yourself, "I've never been good at math," or "My writing is not that good," knock it off. If you say it too many times, you'll start acting the part.
The audio I linked to above is about 15 minutes, but well worth your time. Thanks to Emily for pointing me to this.