This paper reports on a how pre-service teacher use of an online classroom simulation (ClassSim) supplemented existing practicum experiences and contributed to the development of their emerging professional identity. ClassSim was developed to provide pre-service teachers with a safe virtual environment in which they can explore ‘authentic’ and practical classroom scenarios. Users were able to assume the role of a teacher during in the virtual classroom, and during its running time make a number of decisions about the management of the classroom and the organisation of virtual teaching and learning experiences. Embedded tools were designed to enhance the development of connections made between educational theory of their pre-service teacher course and the practicalities of operating in a classroom environment. The data we present in this paper shows how the experience with ClassSim contributed to the emerging professional identity of the users.