Stereotypes are really hard to change. They're reinforced from many sources (media, individuals, groups, etc). But even more than that, stereotypes are schema: they are how we mentally organize information about social groups, and how we can determine whether we are "in" or "out" of a group. Schema allow us to process information effortlessly, and are pretty deeply ingrained once they're there.
The human brain is not very good at changing schema. When we see evidence that contradicts our schema, our brains will do all sorts of mental gymnastics to avoid confronting or changing the incorrect schema. Most frequently, we forget that we saw it all. Sometimes our misconceptions even get stronger .
This happens with stereotypes. Betz and Sekaquaptewa did a study where they showed role models to young girls, to try to motivate the girls' interest in STEM . Role models were either gender-neutral, or feminine. The result? Gender-neutral role models boosted interest -- and feminine (counterstereotypic) role models actually reduced girls' interest in science. To these girls, the feminine scientist -- a stereotype violator -- is aberrant.
Stereotype violators are not viewed favourably by others. Indeed, in laboratory settings, people go out of their way to punish stereotype violators . Stereotype violators are seen as less likable, and less competent. Not surprisingly, women in science are rated as less likable and less competent than otherwise identical men [5, 6].
So, let's say instead of being exposed to just one woman scientist, you are exposed to a bunch of them. Regularly. That will change your schema, right? Nope.
The human brain does a thing that social psychologists call subtyping. Instead of changing your mental model of what a scientist is (white male), you instead create a new category: the woman scientist .
And the evidence is that this is what happens to female scientists, and to female engineers . Furthermore, the stereotype of the woman scientist is of an unfeminine woman. The unfeminine label in of itself is costly: these women are seen as less likable, less attractive, less competent, and less confident .
So how can we change stereotypes, then? It turns out a thing called "perceived variability" is key: it's how much variation we perceive in an out-group . "Out-group" here refers to any group that a person does not identify with; an "in-group" is one that that person identifies with. Humans systematically underestimate the variability within an out-group, particularly in comparison to the variability within the in-group (e.g. men see women as more homogenous than they are; whites see aboriginals as more homogenous; etc).
This is known as the Out-group homogeneity effect. We mentally exaggerate the stereotypical qualities of outgroups (and outgroup members), and ignore the counterstereotypical qualities.
We stop paying attention to stereotypes when we perceive greater variability in the group that's been stereotyped . For example, it's a lot harder to think about aboriginals in terms of generalizations and stereotypes when you're used to thinking about the differences between Inuit, Metis and First Nations, and differences between the Haida, Salish, Blackfoot, Anishinaabe, Innu, Mi'kmaq, Dene, etc.
So how can we increase the perceived variability of an outgroup? Subgrouping refers to the process in which both people members are brought together around common goals or interests, and can include both in-group and out-group members. For example, creating a study group in a computer science class in which both women and men are represented -- or joining a robotics club which has a mix of white, Asian, black, and hispanic students.
Subgrouping "allows for a more varied cognitive representations of group members"  -- it leads you to start seeing the members of your subgroup around their membership in your common subgroup -- rather than their membership in any in-group or out-group. Richards and Hewstone have a very nice literature review about subgrouping and subtyping, showing how dozens of studies have consistently found that subgrouping leads to increased perceived group variability, and stereotype change.
The Contact Hypothesis in sociology gets at subgrouping: the observed effect that being familiar with a member of an outgroup (eg. homosexuals) increases your acceptance of the outgroup. Having a friend, classmate or family member who is queer means you a share with a subgroup with them (friend group, class, family, etc).
For subgroups to form effectively, they need to have meaningful cohesion to those in the subgroup. One study by Park et al that is described by Richards and Hewstone found that they could not form a subgroup around all engineering students: "[they] were all hardworking and bright, but in very different ways. Some were motivated only by money, some by parental expectations, and some by larger environmental goals." Instead, there subgroups of engineering students formed, around those three motivators. 
Similarly, Park et al found that they could not form subgroups around continuous variables (high/moderate/high) or arbitrary bases . And other studies in the Richards and Hewstone review found that trying to form subgroups around having minority status (e.g. clubs for women in STEM, study groups for black students) either did not change stereotypes about their group, or intensified them .
Indeed, I wouldn't be surprised that part of why instructional techniques such as Peer Instruction disproportionately helps female CS/physics students is because they encourage subgrouping. When you have your whole class together, collaborating in small groups for class activities, you're having them bond as classmates -- rather than as members of in-groups or out-groups.
This is one reason I'm always a bit iffy about Women in CS/Science clubs: they don't promote stereotype change, but instead promote subtyping. Instead of changing the notion of what a computer scientist is, they reinforce the subcategory of woman computer scientist.
But stereotypes aren't the only thing that affect minorities. Part of why Women in CS clubs are so popular is that they provide a sense of community to these women. This is really important when you're a minority member! The sense of isolation that many women experience in STEM is why many of them leave.
And, as always, is evidence that girls only schooling can be good for encouraging young girls' interest in math and science . It's somewhat of a tragedy of the commons problem: putting all the women together in a club helps those individual women cope with a culture in which they are negatively stereotyped -- but it doesn't change the actual stereotype.
 Cheryan, Sapna, et al. "The Stereotypical Computer Scientist: Gendered Media Representations as a Barrier to Inclusion for Women." Sex roles 69.1-2 (2013): 58-71.
 McRaney. The Backfire Effect. http://youarenotsosmart.com/2011/06/10/the-backfire-effect/
 Betz, Diana E., and Denise Sekaquaptewa. "My fair physicist? Feminine math and science role models demotivate young girls." Social Psychological and Personality Science 3.6 (2012): 738-746.
 Rudman, Laurie A., and Kimberly Fairchild. "Reactions to counterstereotypic behavior: the role of backlash in cultural stereotype maintenance." Journal of personality and social psychology 87.2 (2004): 157.
 Steinpreis, Rhea E., Katie A. Anders, and Dawn Ritzke. "The impact of gender on the review of the curricula vitae of job applicants and tenure candidates: A national empirical study." Sex roles 41.7-8 (1999): 509-528.
 Moss-Racusin, Corinne A., et al. "Science faculty’s subtle gender biases favor male students." Proceedings of the National Academy of Sciences 109.41 (2012): 16474-16479.
 Richards, Zoë, and Miles Hewstone. "Subtyping and subgrouping: Processes for the prevention and promotion of stereotype change." Personality and Social Psychology Review 5.1 (2001): 52-73.
 Barinaga, Marcia. "Surprises across the cultural divide." Science 263.5152 (1994): 1468-1470.