Scholars posit that descriptive education research that focuses on the instructional dynamic between teachers and students is perhaps one the most salient research topics that can improve learning and teaching. This case study seeks to describe prospective teachers' mathematical affect as they engage in "rehearse teaching" in TeachLivE™, a mixed-reality simulated classroom. Utilizing Goldin et al.'s (2011) engagement structures as evidence of mathematical affect, findings reveal that simulated rehearsals improve prospective teachers' reformed-based teaching and that this improvement may be related to their improved 'in-the-moment' affective states. This study potentially connects prospective teachers' beliefs and emotions as math learners with their behaviors and instructional praxes as novice math teachers. [For the complete proceedings, see ED583608.]