Implementing differentiated instruction through lesson study: reflections from Taiwanese EFL teachers

• Lesson study opened space for DI experimentation in EFL higher ed classrooms. • Peer dialogue helped teachers translate DI from theory into classroom practice. • Flexible grouping proved a practical entry point for DI in large EFL classes. • Teachers grappled with fairness and rigor in differentiated assessments. • Reflective cycles fostered deeper inquiry into instructional decision-making. • Collaborative planning helped demystify DI and build instructional confidence. This study examines how four EFL instructors at a Taiwanese university used lesson study (LS) to explore differentiated instruction (DI) in higher education. While DI is well established in K–12 settings, its implementation at the tertiary level remains limited due to structural, pedagogical, and cultural constraints. This research investigates how collaborative structures like LS can support instructors in developing and applying DI strategies. Using a qualitative design grounded in LS, the study followed seven iterative cycles of joint lesson planning, classroom observation, and post-lesson reflection. Data were collected through field notes and focus group interviews and analyzed using Interpretative Phenomenological Analysis (IPA). The four participating instructors, all with at least five years of EFL teaching experience, had limited prior experience with DI or structured peer collaboration. Findings highlight the value of LS in building shared understanding, encouraging flexible grouping, integrating student choice, and supporting more responsive assessment practices. Teachers progressed from theoretical understandings of DI to more personalized approaches that accounted for student readiness, interests, and learning profiles. However, implementation was constrained by standardized curricula, test-oriented instruction, and concerns about fairness and workload. The study concludes that LS can serve as an effective professional development model for promoting differentiated teaching in higher education. It fosters sustained reflection, reduces professional isolation, and builds teacher confidence through structured peer interaction. Implications for policy and practice include the need for institutional support, dedicated collaboration time, and leadership structures that recognize and reward pedagogical innovation.