Commercial apprenticeship is not only the most commonly chosen type of apprenticeship within Vocational Education Training (VET) in Switzerland, but is also very crucial for educating and training clerks for the Swiss economy. Commercial VET takes place in a VET school setting with practical on-the-job training. VET school teachers' content and pedagogical content knowledge can be crucial for apprentices’ competence development, as existing empirical findings in other domains indicate. The Swiss VET school teachers’ education and training is currently subject of educational reforms. For example, little is known about teachers’ professional education and teaching experience, knowledge, skills, and beliefs. In this presentation I illustrate the measurement of VET school teachers’ professional competence in the commercial field and present first results with data from a teachers’ survey regarding their opportunities to learn and their knowledge.