This paper describes the potential of long-term co-operation between science educators and science teachers concerning the teachers’ continuous professional development, based on Participatory Action Research in science education. The discussion is based on a sixyear case study observing a group of about ten German chemistry teachers by chemistry educators from the university. Substantial changes in teachers’ professional habits and views were found. These findings will be theoretically framed within the Pedagogical Content Knowledge (PCK) debate, a model representing three different modes of action research and the Interconnected Model of Teachers’ Professional Growth (IMTPG). The following discussion will provide an explanation of the changes in the teachers’ professional attitudes and views. This is based on a description of overcoming the participatory approach by addressing essential elements of teacher emancipation. Consequences for classical approaches of in-service teacher training are discussed.