The role of koshi (講師) in lesson study communities: became, being and becoming

Purpose This editorial introduces the special issue on koshi (講師) in communities of lesson studies and explores how individuals came to assume this role (became), how they experience it in practice (being) and how they continue to develop it throughout diversified educational and cultural settings (becoming). Design/methodology/approach The editorial combines narrative reflection with a literature review. Drawing on the editors’ experiences as koshi, relevant scholarship and the articles included in this special issue, it examines the role of koshi through the interconnected ideas of “became, being and becoming”. Findings The editorial argues that koshi should not be understood merely as outside experts or knowledgeable others who advise teachers. Instead, the studies in this special issue portray koshi as professionals who learn through ongoing participation and dialogue, and reflect within communities of lesson studies. “Became” depicts the different, often informal pathways people take to enter the role. “Being” focuses on the relational and context-dependent dimensions of supporting teacher learning, particularly the tensions between expertise and collaboration, while emphasising continued professional reflection. “Becoming” points to the ongoing processes of self-questioning and identity reconstruction through which koshi evolve over time. Across the articles, koshi work appears as deeply relational, culturally situated, shaped through everyday practice and continuously evolving through time. Originality/value This editorial contributes to lesson study scholarship by stressing koshi themselves as learners and developing professionals. By bringing together the editors’ narrative reflections with international perspectives of the authors’ lived experiences, it offers a more humanistic and practice-based understanding of koshi as professionals who continually learn through lessons and learning studies.