The disproportionate attrition of female students in science, technology, engineering, and mathematics (STEM) is well documented in higher education but less well understood at the secondary level. In a large, public high school in an affluent, highly educated city, the high honors mathematics pathway is the only math pathway that has not yet achieved gender parity, an implication for future educational and economic equity. Female students leave this pathway at significantly higher rates than male students, especially during and immediately after the first course of the pathway. Through an explanatory, mixed methods approach, it was found that these female students are not less well prepared than their male peers but they instead use psychological factors to justify their decision to leave--factors related to mindset, stereotype threat, and a fear of failure. These factors include extremely high academic expectations, low self-confidence, increased stress, perfectionist tendencies, outside pressure, and a low intrinsic interest in math-related fields. These results and findings inform recommendations for practice and future research. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]