Since classrooms have become more diverse, professional development on adaptive teaching seems critically important, yet turns out to be complex. Lesson Study may address this issue due to its explicit focus on student learning. In total, 22 Lesson Study participants from different school contexts were interviewed. Clarke and Hollingsworth's Interconnected Model of Professional Growth was used as the analyzing framework to explore its adequacy for understanding teacher professional growth. The results reveal teacher professional growth in adaptive teaching competence and show how the intensive focus on student learning, collaborative professional experimentation and the facilitators' role may contribute to this.

Teachers are expected to address a broad range of diverse pupil needs but do not always feel capable or lack the skills to meet these high expectations. The professional development approach Lesson Study may address this. Therefore, this study examines whether participating in Lesson Study influences teachers' beliefs of self-efficacy and (adaptive) teaching behaviour. A quasi-experimental mixed methods design was used to compare pretest and posttest data of intervention and comparison group teachers (N = 48). Significantly different results between the two groups arise in terms of efficacy in pupil engagement as well as in classroom management and instructional behaviour. Immediate stimulated recall interviews provide insight in these outcomes and illustrate to what extent teachers addressed pupils' educational needs.

Professional school cultures, which can be characterized by teachers who take an inquiry stance and in which exchanging knowledge and collaboratively developing classroom material is common practice, receive increasing attention. However, teachers in many schools still often work in isolation and generally do not critically examine their practices. This could lead to decreased feelings of self-efficacy and could negatively impact teacher learning. To counteract such an isolationist school culture, Lesson Study, known for its integration of collaborative and inquiry-based features, could play an essential role. Using a quasi-experimental design (N = 60) including two questionnaires, this study explores whether participating in Lesson Study influences teachers' perceptions of the school culture and conditions in their schools (such as leadership and collegial support), as well as their feelings of self-efficacy. The results reveal significant between-group differences in terms of efficacy in student engagement and significant within-group differences in the intervention group in terms of teacher autonomy and support from the school department leader as well as all teacher selfefficacy. This study could support school leaders who wish to implement, sustain or upscale Lesson Study practices in order to promote a professional school culture in their schools.