The teacher has very important roles in the classroom, particularly as manager of most resources for learning activities and in providing timely feedback that can enhance learning. But teachers need to be aware of students' achievements and weaknesses to decide how to time feedback. We present MTFeedback, a system that harnesses the new affordances of interactive tabletops to generate automatic notifications about small group collaborative tasks for the teacher in real-time. We deployed the system on a teacher's hand-held dashboard, which supports orchestration of a multi-tabletop environment, the MTClassroom. We validated our approach in authentic (in-the-wild) classroom activities, with 95 higher education students and three teachers across two sets of six classroom sessions. We evaluated the impact of presenting notifications on feedback that teachers provided to students. The notifications were based on qualitative comparisons of students' artefacts against a representation of both expert knowledge and a set of common misconceptions. We demonstrate that our approach can successfully be deployed in the classroom to generate notifications that help the teacher direct their attention more effectively to provide relevant feedback to their students in small group learning activities.