Teachers’ interactions with their students have a significant impact on children’s well-being and development in schools. Unfortunately, teachers often enter the profession unprepared to manage challenging student behavior. As a result, they experience stress that undermines how they interact with students and contributes to exhaustion and burnout. Teacher education programs offer curriculum and training, but these experiences do little to address the underlying psychological processes that make addressing difficult behavior challenging. This study examines whether mindfulness could support teacher candidates by improving their equanimity while managing difficult behavior. Equanimity refers to an even state of mind that is characterized by an open and equal attitude towards experience and people regardless of their pleasantness or unpleasantness. While some argue that equanimity could be an important mechanism by which mindfulness contributes to well-being and mediates prosocial change, it is not yet clear how best to measure and study the effects of equanimity on teaching. This study uses data collected from a brief mindfulness-based intervention with 90 teacher candidates at the University of Virginia to (1) measure equanimity with robust autonomic nervous system and facial affect data and (2) study the effect of mindfulness practice on equanimity and associations of equanimity with teaching practice.