An assumption that knowledge arises from research outcomes has been expanded in recent years to include the possibility that knowledge may also be created from the process of engaging in research. Action research (AR) is particularly well suited to such knowledge development. This article offers a brief overview of knowledge in AR as well as the origins and purpose of participatory AR, and discusses selected contributions to knowledge development published in "Educational Action Research". The author augments the literature with personal learning developed in a research partnership between adults and adolescents. Relational knowledge development was understood through addressing concepts of building trust, being treated like a human being and mental health promotion. Reflective knowledge was built through reflections on the meaning of participating as co-researchers.