Educational psychologists involved in teacher education are expected to develop professional teacher dispositions of preservice students. The professional disposition "teacher as change agent" is used to frame actions in service-learning field experiences in a teacher preparation program. Preservice teacher service-learning journals, self-ratings, participant observations, and mentor teacher reports were used to understand service-learning design elements associated with preservice teacher dispositions as change agents. Frequent service visits extended over time, opportunities to develop relationships at sites, and perceiving that one makes a difference with preschool through high school (P-12) learners were linked to desirable disposition outcomes. Further suggestions for course design elements include (a) providing activities to help preservice teachers understand field contexts, (b) supporting a good match between preservice teachers and learner needs, and (c) making the characteristics and role of change agents part of the preparation and evaluation process. (Contains 1 table and 1 footnote.)