An interesting contribution to the debate over why women shun engineering careers comes from Stanford University's Clayman Institute for Gender Research. We know that girls perform as well as boys in the sciences during the high school years. The separation points appear to be when women declare their majors and even later when women with engineering backgrounds commit to careers.
From the article in the American Sociological Association:
The study found that the real issue for female engineering students is their lack of "professional role confidence." Among other things, this term encompasses people's faith in their ability to go out into the world and be professional engineers and their belief that engineering fits their interests and values, which the study authors refer to as "expertise confidence" and "career-fit confidence," respectively.
"Women engineering students go to the same classes, take the same tests, and get the same GPAs as men, sometimes even higher," said the study's lead author Erin Cech, a Postdoctoral Fellow at Stanford University's Clayman Institute for Gender Research. "But, what we found is that the women in our study developed less confidence in their engineering expertise than men did and they also developed less confidence that engineering is the career that fits them best, even though they went through the same preparation process as men."
As result of these confidence issues, women who begin college as engineering majors are less likely than men to remain engineering majors and less likely than men to believe that they will be professional engineers in the future, Cech said.