This article presents a case study aiming at deepening the understanding of action research as a tool in professional development in pre-service teacher education. The case is the practice of action research in a teacher education programme for secondary school teachers in Norway. While there has been limited research on consequences of inquiry, this article asks how student-teachers experience the process and outcome of doing action research and what we as their teacher-educators can learn from these experiences about facilitating the student-teachers' processes. For most student-teachers the process started with numerous challenges, but in the end the majority experienced a positive outcome. We found that an important condition to ensure that action research functions as a tool for professional development is enough time and space to make it possible to reflect in depth. Familiarising students with research and linking theory and practice seem to need specific attention even after a completed action research project. Reflecting on actions seems to help student-teachers to develop their practical and theoretical understanding in a way that gives their experiences transfer value.