Purpose: This study explores how lesson study (LS) can enhance teacher candidates' ability to develop their pedagogical content knowledge (PCK) for teaching science, technology, engineering and mathematics (STEM). Design/methodology/approach: A multiple case study design was undertaken using the social-constructivist paradigm. The authors explored similarities and differences within and among four cases of teacher candidates who collaborated with a cooperating teacher and a university mentor. The data were collected from field observations, post-lesson discussions and follow-up interviews; it was then content analyzed and validated using negative case analysis. Findings: Learning from post-lesson discussions within their own LS clusters, including a teacher candidate, his/her cooperating teacher and university mentor, could help teacher candidates develop their PCK for STEM, rather than gain experience through several rounds of LS engagement. The foci of post-lesson discussions, which were discussed by each LS cluster the most, were students' context, teaching and STEM prototypes, while knowledge of instructional strategies for teaching STEM was mostly related to the previously mentioned foci. Teacher candidates' confidence in teaching STEM lessons seemed to improve when they designed and discussed the overall lessons with their LS clusters. Originality/value: The STEM-specific LS model was proposed to support the exploration of the struggles and successes of student learning before designing the purpose of the LS and enacting its phases; the implementation of LS could be the tool for enhancing teacher candidates' PCK for STEM teaching.