Past research has demonstrated that mindfulness can protect against the negative effects of stress and ambition on teachers’ burnout. The present study examines whether the protective effects of mindfulness may extend to features of classroom quality; in particular, whether teachers’ interpersonal mindfulness may help them to be emotionally supportive in the classroom, even under conditions of high stress and ambition. Data were collected on a racially/ethnically diverse sample of 224 general education teachers (93% female, 7% male) and their K-5 classrooms. Teachers self-reported on their perceived stress, ambition, and interpersonal mindfulness in teaching, and classroom observations assessed teachers’ emotional supportiveness in the classroom. Linear regression analyses tested main effects of stress and ambition on emotional supportiveness, and teachers’ interpersonal mindfulness as a potential moderator of these effects. Results were partially consistent with hypotheses, suggesting that interpersonal mindfulness buffers against the effects of high stress—but not ambition—on teachers’ emotional supportiveness in the classroom.