In recent years, teacher training has gained significant importance in the implementation of educational, pedagogical, and school policy goals. The professionalism of teachers is to be enhanced, and the development and change processes in schools are to be promoted. To what extent does teacher training meet this demand? This study addresses this question in the context of school development in the canton of Bern. At two schools, the effects of targeted internal training measures are examined. The focus is on the collaboration that teachers are required to engage in with the implementation of the new public school law. Using qualitative and quantitative methods, internal training processes are described, and their impact on teacher collaboration is analyzed. Insights into the realities of schools and faculties lead to conclusions that are significant for future training concepts.