Teachers frequently employ surface-acting strategies to regulate emotions and to be more effective. This can be detrimental for teachers' health but the effects of such inauthentic emotion expressions on students are largely unexplored. In two exploratory studies we investigated the impact of teachers' emotions and emotional authenticity (expressing truly felt emotions) on students' emotions of enjoyment, anger, and anxiety. In study 1 we used generalised (trait-level) assessments from teachers (N = 81) and students (N = 786) on emotions and emotional authenticity. As emotions are dynamic in nature, we further used the experience sampling method with a randomly chosen subsample (N = 128 students) in study 2 to assess momentarily perceived teacher emotional authenticity and students' emotions in the classroom. In study 1 we found teachers' and students' self-reported enjoyment (but not anger and anxiety) to be interrelated. In study 2, all three (perceived) teacher emotions were related to students' emotions. Further, in both studies students' perceptions of their teachers' emotional authenticity related to their own emotions. Although teachers' self-reported and students' perceived emotional authenticity did not converge, the results show that emotional authenticity matters to students. Implications for future studies but also for teachers' emotion regulation are discussed.