This multi-case study compares the experiences of students and instructors participating in three different online discussion formats used to support the collaborative and social aspects of case-based instruction. Data were collected and analyzed from three different universities that implemented case-based discussions or chats in courses as a part of a larger research consortium project. The implementations represented three different discussion group formats for structure and facilitation: open discussions, prompted discussions, and structured chat discussions. Discussion archives were analyzed for number of students who participated, average postings per student, range of contributions per student and instructor facilitation. Follow-up interviews were conducted with a sample of students from each course to assess student perceptions of the benefits and limitations of online discussion groups to augment case-based learning approaches in special education courses. Results supported prior research findings that online chats and discussions provided opportunities for the students to share, discuss, and modify their case understanding and to support each other in using that knowledge to solve case and classroom problems. Practical implications for instructors using discussion groups in case-based instruction are provided. (Contains 6 tables.)