The aim of the current case study is to investigate the master's theses written in 2016 and 2017 by primary school student teachers at a teacher education department in Finland. 111 theses were analyzed focusing on four distinct aspects of the thesis: topic, perspective, research approach and data collection method. The aim is further to discuss how to develop the master's thesis within teacher education in order to promote teachers' professional development. According to the findings, students wrote master's theses of high scientific quality, although an explicit reflection on the relevance and transfer of the knowledge they had gained from the master's thesis to their professional practice did not seem so obvious. The master's thesis is an important part of research-based teacher education and should be developed to encourage students to adopt a research approach in their future work and enhance their profession in this direction.