This study provides a greater understanding of which factors influence the effectiveness of service learning projects at improving graduate students' professional skills. Data for this study was gathered from students in eight Master of Public Administration (MPA) courses taught during two semesters at a large state university. Younger students were more likely than older students to believe that their service learning project was helpful in improving their professional skills. We also find that students who spent more time working on a service learning project outside of class reported their projects were more helpful in improving their professional skills. In addition, our ANOVA analysis indicates that for projects involving group activities, students who were members of groups that worked as teams reported that their projects were more helpful in improving their professional skills than students in less cohesive groups. (Contains 2 notes and 5 tables.)