The need for a more robust, well-trained STEM workforce is becoming increasingly acute in the United States, and there is a clear need to recruit and retain a larger and more diverse population of undergraduate STEM majors. Although numerous efforts to improve engagement and support in the traditional P-16 classroom have been implemented successfully, it is also critical to explore other types of activities that have potential for high impact. The STEM Club Leadership for Undergraduate STEM Education, Recruiting and Success project at our large public research university in the Mountain West presents an outreach model to engage undergraduate STEM majors in developing and facilitating activities in local middle and high school STEM clubs. Through case studies, built on data from reflective journals and semi-structured interviews, the project has identified a number of benefits to the first cohort of participants, which is comprised of 11 undergraduate students operating in interdisciplinary teams across five schools. In this article we describe the essential elements of our outreach model and suggest benefits related to undergraduates' content knowledge, communication skills, metacognition, and identity as a future STEM professional.