Collaboration and collaboration support are often a mixed blessing. While performing tasks collaboratively is useful to gain commitment, shared understanding and to benefit from the knowledge and different perspectives of all participants, it is difficult for groups to work effectively and efficiently. Furthermore, it is challenging to design collaboration support tools and techniques, as not only the requirements of users interacting with the computer, but also the interaction processes among the users and computer interactions need to be considered. In order to support facilitators in monitoring collaboration processes and to suggest process interventions and tool adaptations, we present a first simulation model of a collaboration process. In this model we simulate the impact of group size. Further, we sketch the research agenda to model and simulate collaboration processes. We aim to use these models to compare and evaluate collaboration processes as well as to predict the outcome of possible process interventions and corresponding tool adaptations.