PurposeThe paper focusses on lesson study, which generally engages the collaborative work of a group of teachers, as implemented with a primary school art teacher who had limited opportunities for collaboration. Through lesson study, the teacher worked closely with a lesson study facilitator and an art education expert to plan a research lesson. The study explores how this collaboration generated cognitive conflicts and eventually teacher change.Design/methodology/approachThis paper presents a case study using a thematic approach to data analysis. The lesson study involved weekly face-to-face meetings and daily online communications over a period of eight weeks. In an attempt to reflect upon and resolve conflicts, the teacher kept a journal in which the teacher wrote down lengthy accounts of the discussions with knowledgeable others, the teacher’s struggles and ways of resolving these. Data were complemented by the different lesson plan versions, the post-lesson discussions and a detailed report documenting the lesson study process.FindingsThe paper provides insights into the role that cognitive conflicts play for teacher change. Through ongoing communication, reflection and support to resolve conflicts, the teacher recognised more collaborative opportunities for professional development, freed from rigid lesson planning practices and reported a new conceptualisation to teaching.Practical implicationsDrawing on the literature about effective teacher professional learning, the paper offers implications for supporting teacher change.Originality/valueThis paper provides insights into how lesson study may provide conditions that enable teachers' cognitive conflict and facilitate their consequent resolution.