This study aimed to determine if pre-internship teacher education students' participation in service-learning activities in K-12 classrooms would significantly affect their teachers' sense of efficacy (TSE). A secondary focus sought to determine if one type of service-learning activity (e.g., whole-class instruction) would affect teacher efficacy more than another (e.g., small-group tutoring). Findings revealed that pre-internship service-learners in both types of service-learning activities increased significantly in their TSE. However, neither type of service-learning activity was superior to the other as measured by the minimally accepted 0.05 level. The discussion focuses on factors shared between the two service-learning designs that might mediate a positive mastery experience.