Generalist primary school teachers often have little or no training in school subjects such as science and technology. Not surprisingly, several studies show that they often experience difficulties when teaching these subjects, in fact some primary teachers even avoid teaching them. The over all aim of this study is to contribute to new theoretical and methodological tools for the study of how teachers develop knowledge for teaching, i.e. pedagogical content knowledge (PCK). And based on this, elaborate on implications for the professional development of primary school teachers. The teachers in the study participated in a design-based research project concerning technology education in Grade 1. We were especially interested in whether the teachers displayed any habits that contributed to the development of their personal PCK. We found three significant patterns in how the teachers, together with the researcher, developed knowledge of how to teach a specific topic in technology. We argue that these patterns tell us something about the teachers' epistemic habits in relation to the teaching of technology. The existence of these habits could help to explain how teachers with little or no experience of teaching a subject can develop relevant PCK.