Schools must regularly examine and adapt established practices to address students' and teachers' changing needs (academic, social, emotional, and occupational;Askell-Williams & Koh, 2020). Yet many of the innovations developed to meet these needs fail due to a lack of strategies for implementation (e.g., consistent goal setting), structural prerequisites (e.g., time for planning and implementing innovations), and motivation of school staff (e.g., innovativeness; Cheng & Walker, 2008;Palumbo & Manna, 2019). Theories of organizational change in the school context posit that principals and teachers act as change agents, innovating organizational practices, building collective knowledge around change, and supporting a positive climate for innovations. For this reason, we first assume that teacher collaboration is a key element for organizational change. When teachers collaborate to improve their schools, they can collectively identify the school's needs, develop targeted and effective innovations, and, ultimately, implement innovations. Second, we assume principal leadership is a key supporting factor in teacher collaboration, as principals can ensure that teachers have sufficient time and resources, support in the creation of teacher teams, guide these teams on the process level (e.g., goal-setting), and motivate teachers to achieve the desired organizational changes. Empirical evidence supports this assumption and suggests that principals can involve teachers in decision making relating to the planning and implementation of innovations and can create a caring environment for teachers to change their practices (Fix et al., 2020;Seashore Louis & Murphy, 2017). However, there has been little in-depth research to date on the mechanisms that foster teachers' and principals' collaboration to achieve organizational change. In particular, previous empirical research has not fully investigated the process from planning to implementation of improvement initiatives (Palumbo