Research on teaching and learning puts increasing attention on the expertise of teachers, as it is seen as one constitutive factor of instructional quality. Recent studies used content knowledge and pedagogical content knowledge as predicting variables for expertise in order to explain success in student learning for example. In this work, potential disadvantages of these approaches are analyzed: Managing classroom situations competently needs more than just content knowledge and pedagogical content knowledge. The analysis and description of additional, domain-specific competences is topic of this publication. Therefore, this work proposes a model compatible with existing approaches. It consists of three components of domain-specific competencies: First, a basic component of mathematical and mathematical pedagogical knowledge, second, reflective competencies, and third, action-related competencies. In addition, it is discussed how these three constructs could be operationalized. It is proposed to complement the known paper-and-pencil item formats by video- and computer-based formats in order to increase the validity of tests. Moreover, design and results of a feasibility study with teachers and prospective teachers from secondary level are reported. The results show that in principle it is possible to Measure the three areas of competencies separately.