A prominent phenomenon in education in Europe and internationally is the demand for research-based education, which is also the case in Sweden, the context of this study. Therefore, greater academic demands have been placed on teachers, which can present a distinctive challenge for teachers who were educated when teacher education prioritised practical teacher training rather than academic training. Therefore, it is especially important to explore what and how experienced teachers learn and develop when moving towards a research-based education. The theoretical framework builds on communities of practice and social learning. The empirical data consists of written reflections from 50 teachers in preschool, compulsory and upper secondary school, who participated in action research projects that aimed to help build research-based education. The findings show that the teachers' professional learning entailed changes in the ways they think, act and relate to others in three areas: teaching, research and collaboration. The study offers insights into the importance of a professional development process being based on a bottom-up perspective, collaborative, context-specific and integrated in teachers' work. Lastly, the study points to the benefit of engagement on multiple levels -- principals, lead teachers, teachers and researchers -- to achieve lasting success in building research-based education.