Training systems with intelligent virtual agents provide an effective means to train people for complex, dynamic tasks like crisis management or firefighting. Virtual agents provide more adequate behavior and explanations if they not only take their own goals and beliefs into account, but also the assumed knowledge and intentions of other players in the scenario. This paper describes a study to how agents can be equipped with a theory of mind, i.e. the capability to ascribe mental concepts to others. Based on existing theory of mind theories, a theory-theory (TT) and a simulation-theory (ST) approach for modeling agents with a theory of mind models are proposed. Both approaches have been implemented in a case study, and results show that the ST approach is preferred over the TT approach.