This paper presents the experience of a group of teachers who have developed action research (AR) dynamics for 15 years aimed at their professional development and teaching practice improvement. The focus is first on the importance of AR, collaborative dynamics and theory and practice relationships for in-service teacher training. It also shows the different spiral and cycle stages carried out, as well as the group's characteristics, its evolution during these 15 years and the annual operation structure currently in use. The results show the five large AR thematic spirals developed and the materials generated and disseminated. There is also an analysis of the main benefits and problems so far encountered. Finally, a series of reflections and conclusions on the implications of keeping such a workgroup for so long is detailed. (Contains 5 tables.)