Teaching science through inquiry is regarded as a means to enhance students’ learning through facilitating the learners’ understanding of science concepts, skills of scientific inquiry and understanding of the Nature of Science (NOS) (NRC 2000; Sadler et al. 2010; Schwartz & Crawford 2006). Nevertheless inquiry, in the form of inquiry-based teaching and learning, rarely finds its way into the classroom and if it does it frequently takes place in a teachercentered manner and not as was intended, as open inquiry, where the students gain the ownership on the research question, the research process and the outcome. One major obstacle is that open inquiry demands an often un - familiar and challenging role for the teachers (De Jong & Van der Valk 2007; Furtak 2008; van der Valk & de Jong 2009). Instead of teaching by providing explanations as would normally be the case, teachers instead support the individual learning processes of students who carry out their own investigations, starting from their individual research questions. The teachers’ role has to change from instruction to coaching. In order to support the teachers in their professional growth in the field of Inquiry Based Science Education (IBSE) and in their developing self-confidence in conducting student-centered approach to IBSE, we argue that more specific support in pre-and in-service teacher education must be provided. With this goal in mind, we developed a professional development course for open inquiry. To operationalize the professional development processes for our research we employed the concept of Pedagogical Content Knowledge (PCK). Being teacher educators, course developers and educational researchers at the same time, we were using an action research approach for our own investigation. In our model the action research in question has been conducted by the teacher educators, and the participating teachers have been involved through intensive reflective cycles referring to their teaching in all phases of the course, but in this approach the teachers themselves do not conduct action research themselves by collecting and analyzing data.