At both the national and international levels, teacher collaboration has emerged as a crucial condition for professional development in education. Furthermore, its positive impact has been underscored not only on student learning, but also on teaching practices and the overall educational environment. This paper presents the findings from an instrumental qualitative case study focused on Chilean primary and secondary school teachers participating in a collaborative problem-solving professional development programme (PDP) that lasted for a year and a half. With the aim of fostering sustainable change in teacher collaboration, the programme involves collaborative planning, implementation, and reflection. Using activity theory as an analytical lens, we illustrate how the PDP acted as a catalyst for the evolution of teacher collaboration, advancing it from initial and informal approaches towards more profound and systematic collaboration. We highlight the relevance of certain characteristics of the educational community and its norms in shaping an environment that is conducive to teacher collaboration, and we also explore the conditions and possibilities that give rise to teacher collaboration within the context of a professional development programme.