Scientific American Mind has an article online about Stereotype Threat — the idea that we take on and act out the stereotypes we think others have of us.
As it turns out, research shows that such performance failures cannot always be attributed simply to inherent lack of ability or incompetence. Although some have jumped to the highly controversial conclusion that differences in attainment reflect natural differences between groups, the roots of many handicaps actually lie in the stereotypes, or preconceptions, that others hold about the groups to which we belong. For instance, a woman who knows that women as a group are believed to do worse than men in math will, indeed, tend to perform less well on math tests as a result.
The same is true for any member of a group who is aware that his or her group is considered to be inferior to others in a given domain of performance—whether it is one that appears to tap intellectual and academic ability or one that is designed to establish athletic and sporting prowess.