This study compared "Structured Controversy" (a semi-formal debate like small group activity) with a traditional open discussion format for medical and physical therapy students. We found that those students who had participated in Structured Controversy changed their personal opinion on the topic more than those who were in the Open Discussion groups. Students in the Structured Controversy group also commented more often that being "forced" to explore both sides of the topic made a difference to their learning. We conclude that the time and effort invested in organizing the Structured Controversy experience for students is worthwhile because it encourages students to more seriously consider many aspects of an argument and helps promote sustained change of opinion. (Contains 3 tables and 1 figure.)