DARWARS is envisioned to be a virtual training environment in which multiple distributed individuals will interact with each other and with synthetic entities to in order to acquire operational skills. Training in teamwork skills will be a significant component of the DARWARS experience. In particular, DARWARS will provide the capability for training multiple teams of players at the same time, where the teams will interact in a variety of ways, thereby providing training opportunities for a wide variety of skills. Accordingly, DARWARS faces a significant challenge in assessing teamwork skills as players interact with the simulation and with each other, and in providing that assessment to players in the form of coaching during a training session or feedback in an After Action Review (AAR). Assessing the performance of distributed teams in a simulation-based environment faces three major challenges: (1) creating situations in which the relevant teamwork skills are appropriate; (2) measuring behavior in these situations; and (3) providing assessment to learners at the appropriate moment and the appropriate level of detail. This paper will review our methods, discuss the measures most relevant to DARWARS, and present an example of teamwork measurement in a multi-player commercial game scenario designed to teach teamwork skills relevant to military teams.