This article discusses specific examples of virtually mediated interactions involving two transatlantic groups of student-teachers who engaged in a task-based telecollaborative project for the purposes of a teacher education course. The Vygotskyan framework of learning and development and particularly the construct of Zone of Proximal Development (ZPD) in a collaborative frame serve as the theoretical basis of this study. This article aims to: (1) analyze the essentially language-mediated interactions to trace instantiations of virtual collaboration developmentally (2) discuss teacher learning outcomes of the (tele)collaborative activity, and (3) examine learning as expansion of what was explicitly proposed as objectives of the course, resulting from reasoned action i.e., reflection on the process and outcomes of the activity. The findings suggest that the effective integration of telecollaborative activities in pre-service teacher education programmes can enhance teacher learning in significant ways.