Purpose: Lesson study (LS) is a collaborative form of action research. Collaboration is central to LS methodology, therefore exploring and expanding the understanding of the collaborative features that occur in LS is a priority. This paper explores the features of collaboration in existing publications on LS to consider if, as Quaresma (2020) notes, collaboration is simplistically referred to within LS research. Design/methodology/approach: Utilising a qualitative review of LS literature to explore LS collaboration through Mynott's (2019) outcome model and Huxham and Vangen's (2005) theory of collaborative advantage and inertia. 396 publications using "lesson study" and "collaboration" as key words were considered and reviewed, with 26 articles further analysed and coded, generating a collaborative feature matrix. Findings: While collaboration in LS is referred to generically in the articles analysed, the authors found examples where collaboration is considered at a meta, meso and micro level (Lemon and Salmons, 2021), and a balance between collaborative advantage and inertia. However, only a small proportion of LS publications discuss collaboration in depth and, while the matrix will support future research, more focus needs to be given to how collaboration functions within LS. Originality/value: Through answering Robutti "et al."'s (2016) question about what can be learnt from the existing LS research studies on collaboration, this paper builds on Mynott's (2019) outcome model by providing a detailed matrix of collaborative features that can be found in LS work. This matrix has applications beyond the paper for use by facilitators, leaders of LS, and researchers to explore their LS collaborations through improved understanding of collaboration.