The analysis of case studies is an important constructivist instructional strategy that shows potential for engaging students in asynchronous online discussions. However, little is known about the use of audio-based discussions to promote this type of analysis. Twenty-nine students from two sections enrolled in an online instructional design course participated in the study. Students from both sections had the opportunity to experience different learning activities including online case-based discussion forums using text-based (Moodle) and audio-based (VoiceThread) formats. Data from a course evaluation survey were collected and analyzed based on the diffusion of innovation theory. Results revealed that students considered the case-based discussion as the most relevant learning activity. Additionally, students preferred the text-based format over the audio-based for the discussion of case studies. Reasons for their preferences and implications for research and practice are discussed.