In this ongoing study, the focus is put on the potential influence of specific knowledge on pre-service teachers’ judgment processes when diagnosing the difficulty of mathematics tasks. It is assumed that pre-service teachers use their knowledge in order to identify difficulty-generating task characteristics and to evaluate them in terms of their difficulty for students. To examine this assumption, an experimental group, in which participating pre-service teachers acquire knowledge about typical student difficulties and specific difficulty-generating task characteristics is compared with a control group. Using eye-tracking technology and stimulated recall interviews, indicators for diagnostic judgment processes are collected and compared between conditions. First results suggest that specific knowledge leads to a more efficient judgment process and enables pre-service teachers to identify and correctly evaluate difficulty-generating task characteristics more frequently.