This convergent mixed-methods study aimed to evaluate the mentorships in a high school with well-established student mentorship opportunities. Examining the characteristics and role of mentorships for students interested in Science, Technology, Engineering, and Math (STEM) careers determined how mentorships impact STEM career decisions. Quantitative analyses through binary logistic regression, chi-square tests, and independent t-tests uncovered characteristics of mentorship completers and completers interested in STEM careers. Completers were more likely to be female, did not have an Individualized Education Plan (IEP), were not enrolled in the Free and Reduced Lunch Program (FRLP), and finished more math and science courses than non-completers. Completers who expressed interest in STEM careers were more likely to be male, and finished more math and science courses compared to those who did not express interest in STEM careers. Qualitative data analyzed from 15 interviewees interested in STEM careers showed that completers were more likely to use resources, had greater career specificity, and had stronger STEM self-efficacy than non-completers. The results from this study can help STEM educators and school districts find methods to support students pursuing STEM careers. Potential mentorship program improvements included enhancing the accessibility and completion rate of student mentorships, enriching the meaningfulness of mentorship experiences, and simplifying the mentorship obtainment process. Implementing the changes above to mentorship programs aids in developing future STEM workers. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]