The use of augmented reality (AR) to support the learning process has been extensively researched but its use to support the teaching practice has just started to be explored. In this paper, we present a communication system that makes use of a pair of Google Glass to provide the teacher with a constant and private flow of information on the students' current knowledge. The proposed system allows the information sent by the students through their mobiles to overlap with the teachers' live vision of the class. Compared to other feedback systems like clickers or backchannel systems, this AR prototype avoids teachers diverting their gaze and interrupting the class to access the students' feedback. This supports the constant monitoring of potential comprehension problems that might otherwise be overlooked. With the aim of obtaining insights on the teachers' and students' views of the system, we conducted two studies during which the system was used in real classroom settings. The results of both studies suggest that the AR system could report benefits in terms of better communication between students and teachers, and a more adequate rhythm of the class. Also, the use of the AR system in the classroom does not necessarily constitute an element, which will distract and disrupt educational activity.