Teachers play a critical role in bullying prevention but often struggle to identify bullying and intervene effectively, particularly in real time and in the classroom. The coaching literature suggests that ongoing, tailored supports are often needed to promote changes in teacher practices. The purpose of this study was to examine the efficacy of an adapted version of the Classroom Check-Up (CCU) coaching model, which utilized mixed reality simulation to allow teachers to practice addressing the detection of, prevention of, and responding to bullying in the classroom. The sample included 78 teachers within 5 middle schools, randomized to either receive coaching or serve as a comparison teacher. Teachers provided survey data regarding their perceptions about the occurrence of bullying and how they respond to bullying. Classroom observations of teacher preventive and responding practices as well as student aggression were conducted by trained observers. Regression analyses examining differences between intervention and comparison teachers, following coaching provided during one school year, indicated that intervention teachers were more likely to report responding to bullies with referrals to counselors and other staff, to intervene with the victims and perpetrators, and report that they do not perceive adults at their school do enough to address bullying in schools. Survey data regarding detection approached significance; however, observational data regarding preventive practices and responding showed no differences. Together with prior research findings showing that the intervention was acceptable and feasible, these results demonstrate the promise of this preventive intervention for increasing teachers' responding to and detection of bullying in classrooms.