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 self-efficacy. 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.