Background: Developing collective professional capacities in schools is important for school improvement, and principals can initiate such developments. That is, by initiating and leading professional group discussions on teaching and learning, principals can influence teaching practices and, thereby, indirectly affect student outcomes and school improvement. However, research indicates that leading such discussions in communities of professionals can be a challenge for principals. Purpose: The aim of this article is to explore and yield insight into how a conceptual model (the LPGD model) can support principals in guiding professional group discussions on school development and change. Method: The study adopts a qualitative observational approach. Data were collected through observations of a pilot use of the model by principals who participated in the National School Leadership Programme in Norway. The data analysis was guided by cultural-historical activity theory (CHAT). Findings: The analysis shows how the conceptual model can help school leaders to guide group discussions, especially when creating a shared understanding of the problems at hand and building collective commitments that are essential to improving teaching and learning practices. Conclusion: This article highlights the need for school leaders to be supported to develop certain skills to lead professional discussions on school development -- in particular, skills to help leaders in building a shared understanding of problems and collective commitments that are essential when improving teaching and learning practices.