In previous studies on Supplemental Instruction (SI) relatively little attention has been paid to the “senior” students who lead the sessions. The focus in this study is on the benefits that the SI leaders gain from their SI experience. Data from one questionnaire directed at 35 students who recently completed their assignment as SI leaders, and another questionnaire directed at 20 former SI leaders who have graduated and are currently employed, was analysed. The results indicate that the SI leaders improved their communication and interpersonal skills, several types of leadership skills, and self-confidence as well as acquiring a “deeper” understanding of course content. However, the majority of the SI leaders do not seem to have changed their way of studying or their approach to planning their work, based on their SI experiences. A majority of former SI leaders regard their SI leader experience as an important asset in attaining employment after graduation. A clear majority of former SI leaders have had some use, or good use in their later professional life, for skills acquired and developed during their SI leadership.