Facilitating discussions is a key approach that science teachers use to engage students in scientific argumentation. However, learning how to facilitate argumentation-focused discussions is an ambitious teaching practice that can be difficult to learn how to do well, especially for preservice teachers (PSTs) who typically have limited opportunities to tryout and refine this teaching practice. This study examines secondary PSTs' perceptions and engagement with a science performance task--used within an online, simulated classroom consisting of five middle school student avatars--to practice this ambitious teaching practice. Findings showed that the PSTs had a strong understanding of the discussion's primary goal and perceived the task components to be easy to understand, useful in helping them prepare for the simulated discussion, and an authentic representation of what middle school students would say and do. In addition, while the PSTs attended to similar content and pedagogical features within their facilitated discussion, they varied in their ability to successfully facilitate the discussion. This study adds to the growing literature on innovative, technology-based solutions for supporting teacher learning and points to one productive approach that can be incorporated within science teacher education as an approximation of practice of this ambitious teaching practice.