Background: Women are underrepresented in science, technology, engineering, and mathematics (STEM) professions. Even the most promising female students' interest in STEM subjects often decreases during secondary school. Using the framework of the Social Cognitive Career Theory, the present study examined the influences of social agents in female students' persistence in STEM. Specifically, the present study used a retrospective survey investigating the influence of parental education, teachers as mentors, and peer belonging for female students' attainment of an undergraduate degree in a STEM field for a special population--female graduates of selective science high schools (n = 1425). Furthermore, the study examined the influences of these social-agent variables on female students' STEM choices when mediated by high school research experiences. Finally, the present study also explored the influences of these social-agent variables on female students when it came to choosing math-intensive STEM fields (n = 723). Results: Findings showed that parental educational level and having STEM teachers as mentors are positively related to female students' later attainment of a STEM degree. In addition to the direct relationship, parental educational level and having STEM teachers as mentors are also positively related to female students' high school research participation, which is associated with a greater likelihood of their completing a STEM degree. Female students' sense of belonging to a peer group did not correlate with their attainment of a STEM degree. When it came to choosing math-intensive STEM fields, a higher sense of peer belonging was negatively associated with obtaining a math-intensive STEM degree. Conclusions: Parental education and having STEM teachers as mentors play an important role for female students' persistence in STEM and obtaining a STEM undergraduate degree for female students in selective science high schools. However, among the female students who graduated with a STEM degree, it is less clear whether social-agent variables influenced their math-intensive vs. less-math-intensive choices. Educational implications for promoting female students' STEM interests and careers in STEM fields are provided.