In this paper, we present a case study of a beginning chemistry teacher who enrolled in a project aimed to contribute to the development of teachers' knowledge of models and modelling in science. The project consisted of a series of institutional meetings in combination with an action research project the teacher conducted in her own classes. By explaining how the project was conducted and mainly by focusing on the teacher's voice, her dynamic, continuous, and non-linear process of knowledge development is discussed in detail. We were able to investigate and describe this development in terms of various types of knowledge--content knowledge, curricular knowledge and pedagogical content knowledge--which were developed simultaneously. Among other results, it became clear how certain institutional activities led to specific choices in the teacher's action research project. For instance, although initially she was reluctant to conduct a modelling activity in her class, she decided to experiment with such an activity in her action research project. Subsequently, the responses of her students during the project convinced her of the value of this modelling activity and helped her to become aware of specific views of her students. Finally, it became evident that the whole experience made her very enthusiastic and stimulated her to formulate specific intentions with respect to the future, both in terms of applying certain teaching activities and in terms of collaborating with colleagues.