This study was undertaken to better understand the nature of preservice teachers' reflective thinking during case discussions about classroom management in two online formats: synchronous versus asynchronous. Findings indicated that when participants engaged in synchronous online case discussions they had higher levels of critical reflection than when they engaged in asynchronous online case discussions. Also, participants' initial preferences for asynchronous discussions changed from the beginning to the end of this study. Reasons for changes in participants' format preferences and descriptions of participants' levels of critical reflection are discussed.