Science Olympiad is a K-12 science, technology, engineering, and mathematics (STEM) competition that engages approximately 7,000 teams across the U.S. in individual and team challenges at regional, state, and national levels. Science Olympiad began expanding to include elementary students in 2008. Yet, little is known about the adults who volunteer to coach elementary Science Olympiad teams or their coaching motivations. The purpose of this study was to investigate who coached elementary Science Olympiad teams, what motivated them to volunteer, and how their participation influenced their science teaching self-confidence, knowledge, and practices. This mixed-methods study investigated 125 Elementary Science Olympiad coaches' beliefs in the southeastern U.S. Survey items were based on the Coach Motivation Questionnaire (CMQ). Open-response questions following the survey items were coded in two ways; inductively and based on a priori motivational codes. Participant coaches were most likely to be teachers (92%), female (85%), and White (85%). Survey findings indicate that coaches' most significant motivating factors were intrinsic (M = 4.33/5); minor differences were based on gender, role, and length of time coaching. The qualitative responses supported the survey findings and gave more insight into teacher-coaches' thinking. The coaching experience had many positive effects on the teachers, such as enhancing their science and pedagogical content knowledge in science and other subjects, strongly influencing their self-confidence, and increasing their use of hands-on science and STEM activities.