Human-in-the-loop simulation is a valuable tool that can support novice teachers in learning how to lead classroom discussions. We ground our use of simulation in a theory of practice-based teacher education, examining how authenticity is theorized around approximations of practice. We then illustrate the use an approximation of practice approach, discussing guiding principles of project work in which novice teachers learn to facilitate small-group discussions with digitally simulated fifth-grade students. Several provocative vignettes illustrate the complexity of authenticity, suggesting additional theorization to help us authenticity as more a malleable attribute than as simulation's end goal. One implication is that more study is needed, in the context of using virtual environments and humans in teacher education, addressing authenticity, participant perception of authenticity, and their interaction.