The quality of teaching is significantly enhanced through feedback to teachers about their teaching. Whereas systems to show student learning exist, those showing the emotional state of the classroom do not. We argue that such systems could greatly improve teaching, and in consequence, pupil attainment. Data for such systems could come from biometric sensors or from cameras and microphone monitoring the gaze of students, their restlessness, and the level of noise in the classroom. Such systems would be valuable in particular for teachers with less experience.