While in many countries scientific topics at the primary school level are taught in two subjects – social sciences and sciences, Germany provides one subject only: among others disciplines like physics and history are integrated into one subject called Sachunterricht. The wide variety of scientific disciplines within one subject requires teachers’ professional knowledge in all involved disciplines. In contrast to that, depending on the university, teacher students either focus one discipline in depth, or, receive an overview of natural or social science. The consequence of this education is that teachers leave university with knowledge only in some parts of Sachunterricht. Simultaneously, it should be examined if teachers can compensate deficits by teaching experiences. In order to examine the relationship between teachers’ educational background, teaching experiences and professional knowledge in Sachunterricht, the present study aims at comparing professional knowledge of teachers with different educational backgrounds and degrees of experience. The content ‘combustion’ is used as frame for examining professional knowledge. This study has been carried out using the data collected from a sample of 203 teachers. The sample is divided in different teacher groups: teachers with natural science education, teachers with social science education and teachers who had no education in Sachunterricht. To consider the influence of teaching experience, the groups include experienced and non-experienced teachers. Altogether, the results show that teachers who teach the content ‘combustion’ should be educated in natural sciences.