Institutions of higher learning generally seek to provide students with experiential learning, professional development, and tools for contributing to a diverse global society. However, many students are not able to connect their learning to their career interest. As a result, graduates do not feel confident that they have acquired the job competencies to be successful when entering their profession. The purpose of this study was to investigate how to guide student supervisors in providing mentorship that develops career competencies and self-efficacy of undergraduate student employees. The functions of mentoring (career development, psychosocial support, and role modeling) were used as a guiding framework for the various behaviors supervisory mentors can demonstrate to engender positive results for their direct reports. The following research questions were explored: "(1.) What can be learned at individual, group, and system levels that advances theory and practice in an action research project guiding supervisors in developing career competencies of student employees?" "(1a.) What impact does a mentorship program have on developing career competencies and self-efficacy of undergraduate student employees?" "(1b.) What impact does a community of practice have on student supervisors?" The action research study involved three cycles, including (1) critical incident interviews, (2) a mentorship program between undergraduate student employees and their supervisors, and (3) a community of practice with student supervisors. Quantitative data included questionnaires administered pre- and post- interventions and qualitative data included participant interviews. Findings showed that supervisors need support and resources to effectively develop career competencies of student employees. When supervisors can balance the mentoring functions of career support, psychosocial support, and role modeling, student employment can serve as a high-impact experience for development. Institutions should invest in holistic and immersive programs that enhance the student employment experience not only for students, but supervisors as well. [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.]