PurposeThe purpose of this study is to explore mathematics teachers' collaboration within their professional learning communities (PLCs), and to gain insight into how the teachers developed their collective efficacy through it to focus on improving student learning.Design/methodology/approachUsing a qualitative approach, data were collected from three high-performing secondary schools, mainly through semi-structured in-depth interviews with the Heads of Mathematics Unit. For explication and triangulation purposes, focus group interviews with the mathematics teachers and students and document analysis were also conducted.FindingsThe findings indicate that PLCs were the vessel through which a culture of disciplined teacher collaboration was fostered. More importantly, this culture encouraged teachers to participate in reflective dialogues that became a driver for their learning, and eventually led to their changed professional practice for improved student learning. The collaborative setting within the PLCs allowed teachers to pool their resources, knowledge and individual expertise to identify their student learning focus, and administer and measure their student intervention strategies. This collaborative professional learning reduced professional isolation, and as a result, improved teachers' collective pursuit of professional growth to impact student outcomes.Research limitations/implicationsThe aim of this qualitative study was to provide a detailed description of the teachers' collaboration within their PLCs based on the researchers' interpretation of how the participants make sense of their PLC practices and experiences. Hence, findings are indicative, and not definitive. In addition, the Heads of the Mathematics Unit, and the mathematics teacher participants in this study illustrated salient aspects of subject subcultures, where their beliefs, norms and practices were non-generic, or specific only to their subject context. Therefore, the implications to practice were built from commonalities shared only among the mathematics units.Originality/valueThis is a study in a Malaysian context that provides empirical evidences that are concerned primarily with the process of teachers developing their collective efficacy through disciplined collaboration within their PLCs.