Explicit (i.e. conscious) primary school teachers' beliefs on computer science were gathered through semi-structured interviews and analysed using the grounded theory methodology. Implicit (i.e. unconscious) beliefs were inferred upon while observing computer science lessons given by the interviewed teachers in their classroom on one of the following topics: introduction to programming with the bee-bot®, introduction to programming with scratch®, and cryptography. A pre-post-comparison was conducted with a closing interview. Analysis of the data revealed four distinct views on computer science: media-oriented, mathematical, social, and design-oriented. Furthermore, the study showed that the teachers' beliefs could in some cases be altered by the computer science lessons. Some teachers, however, showed resilience towards conceptual change (belief perseverance). The study was conducted in the state of North Rhine-Westphalia (Germany) and included ten participants for the initial interviews and three participants for the lessons and closing interviews.