Teachers’ diagnostic competence includes the ability to identify misconceptions in student solutions and to respond adaptively to these solutions. The present project focuses on such situations and aims at the systematic analysis of the influence of situation characteristics (with/without time pressure) on diagnostic judgement processes of persons with different personal characteristics (pedagogical content knowledge, professional experience). The judgment processes are described in terms of the DiaCoM framework as information processing in which the information to be processed results from a) situational cues and b) the teacher’s knowledge structure. The cues are student solutions that indicate a particular misconception in the area of fractions, as well as more or less relevant features of tasks on fractions. With regard to the teacher’s knowledge structure, pedagogical content knowledge about misconceptions and task characteristics is particularly important. According to Brunswik’s lens model (1995) and the DiaCom framework (Loibl et al., 2019), a teacher’s judgment regarding the most adaptive responses in a specific diagnostic situation is assumed to depend on which of the presented information she perceives and how she uses her pedagogical content knowledge to process that information. Information processing is expected to be influenced both by the availability of episodic experiences (e.g., Leinhardt & Greeno, 1986; Putnam & Borko, 2000) and by time pressure (dual-process theories, e.g., Kahneman, 2000, cf. Rieu, Loibl, Leuders & Herppich, in press, for judgment processes in difficulty estimation with and without time pressure). To document the judgment processes, not only the selection of the most adaptive teacher responses but also protocols for thinking aloud are recorded and eye movements are tracked.