Isabell Bausch develops and describes a practical measurement instrument for capturing profession-related competencies of mathematics teacher education students. The instrument TELPS (Teacher Education Lesson Plan Survey) was used between 2009 and 2013 at TU Darmstadt and the University of Technology Sydney to investigate the development of mathematics didactic knowledge in lesson planning. The author reports both cross-sectional and longitudinal results and uses these to create a web application. This application generates automated feedback on the captured mathematics didactic knowledge, thereby supporting competency acquisition in different phases of training. The chosen development approach using the Repertory Grid method also offers the possibility of transferability to other subjects.