Although the Master of Arts in Teaching English to Speakers of Other Languages (MA TESOL) practicum course is meant to initiate preservice teachers (PSTs) into the TESOL profession, it is not uncommon for PSTs to feel a high level of stress as they prepare to teach their first solo lesson. This article proposes the implementation of mixed-reality simulations, in which PSTs teach student avatars- computer-generated 3D representations of real-life students displayed on a computer or large screen--as a precursor of the first solo lesson. In contrast to other fields, in which mixed-reality simulations have been used for some time, their use in MA TESOL teacher preparation is more recent (Kamhi-Stein et al., 2020). This article describes Mursion, a mixed-reality simulation platform, identifies the principles supporting the integration of mixed-reality simulations in MA TESOL teacher preparation, and discusses the benefits and challenges arising from their implementation.