The level of professionalism among German teachers, the deficiencies in teaching, and the lack of knowledge among young people at the end of their schooling frequently dominate headlines and media talk shows. International comparative studies catalyze the search for the causes of educational stagnation. However, the issue of teaching subjects outside of one's area of expertise is rarely discussed. It has never been the focus of scientific publications and is seldom addressed by education policy. As a result, many parents and students are not even aware that teachers, especially in primary, secondary, and vocational schools, often have to familiarize themselves with the content they teach and that they have been teaching subjects for years that they did not study. Carsten Schufft consolidates the fragmented state of research into an overview and discusses the results of his work.