Differentiated instruction has been advocated for embracing learner diversity, but it has been found that differentiated instruction implementation is difficult and teachers often feel unprepared. This qualitative case study explored the professional development of two English language teachers in two participating schools of a school-university collaboration project on diversity management in Hong Kong. Based on the data collected from co-planning meetings, lesson observations, semi-structured interviews, focus groups and artefacts, the study showed that research-informed teaching and teaching-informed research were both indispensable to differentiated instruction infrastructure building; school cultures and teacher efficacies both affected teachers’ attitudes towards researcher-practitioner collaboration modes for professional development. Teachers whose efficacy and professional learning community remained at a developing stage tended to rely on an expert-guided collaboration mode. Yet, those whose efficacy and professional learning community had advanced would prefer a more self-redirected learning mode. These findings shed light on bridging the researcher-practitioner divide in teacher education. Copyright © 2024 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.