Objective: To compare the effects of active and didactic teaching strategies on learning- and process-oriented outcomes. Design: Controlled trial. Setting: After-hours residents' teaching session. Participants: Family and Community Medicine, Internal Medicine, and Pediatrics residents at two academic medical institutions. Interventions: We randomly assigned residents to two groups. One group received a didactic lecture on effective use of diagnostic tests; during this session, the teacher spent a full hour delivering content. The other group received the same content in a session structured to foster resident-to-resident interactions. In the latter session, the teacher spent only 30 minutes directly delivering content to residents. Measures and Main Results: We measured residents' knowledge about and attitudes toward the session content before, immediately after, and one month after each session. We measured residents' perceptions of engagement and session value immediately after each session. We employed blinded observers who used a structured instrument to observe residents' activities during each session. Both teaching methods led to improvements in residents' scores on both knowledge and attitude assessments. The amount of improvement was not statistically different between groups. Residents in the active learning session perceived themselves, and were observed to be, more engaged with the session content and each other than residents in the didactic session. Residents in the didactic session perceived greater educational value from the session compared to residents in the active session. Conclusions: We reduced the amount of time spent in teacher-driven content delivery by 50 percent and covered the same amount of content with no detrimental effects on knowledge acquisition or attitude enhancement. Teaching strategies that foster learner-to-learner interactions will lead to more active engagement among learners, however, these learners may value the session less. Further research is needed to explore learner perceptions of the teaching process and other outcomes of active learning in medical education.