Referencing an Ed Week article:

Stanford University psychologist Claude M. Steele made headlines in 1995 with a study that introduced the phrase "stereotype threat" into the national lexicon. Put simply, it’s the idea that people tend to underperform when confronted with situations that might confirm negative stereotypes about their social group.

Jim Horn writes in the excellent Schools Matter blog:

Could there ever be devised a more consistent, hammering confirmation of stereotype for minority children and parents living economically disadvantaged lives: the more you struggle, the steeper the hill gets over time, and the more likely you are to fail the high stakes tests on which NCLB is built?

It is sadly interesting to note, too, that now as we finally start talking about interventions to address stereotypes and the achievement gap, there is a focus almost entirely on psychological interventions--as if the poverty that drives the achievement gap can be fixed by tinkering inside the heads of students and teachers. While surely the psychological space is critical in terms of shaping learning and education, fixation on the psychological can lead to a debilitating blindness to the equally-strong sociological realities that shape children's lives.

Ed Week requires subscription. For some background information on Stereotype Threat try the Wikipedia entry.