In this study, we explore the role of boundaries for collaborative learning and transformation of work practices to occur. We report from a three-year action research project including well over 1800 h of participation by the authors. The empirical data are based on project participation work including observations and field notes, project reports, interviews and a questionnaire, within a school development project in Nordic elementary school. In the project, teachers and researchers from three Nordic countries, Norway, Sweden and Denmark, collaborated to develop novel, on-line teaching models for a Nordic Virtual Classroom. The virtual classroom refers to an educational setting where teaching and learning activities are conducted collaboratively in cross-national teams "in the cloud" by means of information technology. During the project, teachers were challenged in their current teaching practices and the project resulted in collaborative learning and transformation of work practice. In this paper, we explore underlying reasons for such transformation to occur by unpacking how and why boundaries can play a role in computer-supported collaborative teaching and stimulate a transformation towards digitalized teaching practices. The paper contributes with an explanation of how the composition of boundaries of a technological, organizational, and cultural nature operates and constitutes a resource for learning and principles for how boundaries can be used for such purpose.