One of the main challenges for teachers during teaching in class is the diagnosis of students’ learning and thinking processes. For this purpose, teachers must perceive relevant information, they need to interpret this information and finally, they need to respond and select suitable opportunities to learn. In this paper, diagnostic processes in classroom situations are analyzed on the basis of a video test that was used in a follow-up study of the Teacher Education Development the so-called TEDS-FU Study dealing with early career primary teachers. The results point out that teachers cope with diagnostic tasks during teaching very differently. Varying perspectives in perceiving and solving diagnostic situations can be reconstructed such as a content-related mathematical perspective on the one hand and a student-related, more pedagogical perspective on the other hand.