Large-scale live training exercises require significant funding investments in personnel, equipment, and other resources. Given the current state of budget constraints, Simulation-Based Training (SBT), specifically, Game-Based Virtual Environments (GBVE), represents an opportunity to alleviate such challenges. However, from the SBT perspective, scalability (e.g., the number of simultaneous trainees supported) and flexibility (e.g., resources required to build and render new scenarios, real-time scenario adaptation) hinder the ability of GBVEs to address large-scale training. Virtual Worlds (VW) offer a viable solution to resolve the challenges facing the U.S. Army's existing training paradigm. Emerging research in the field of VW training for operational tasks seeks to understand where in the training cycle such technology is most beneficial, how to implement such capabilities, in addition to the return on investment. The U.S. Army Research Laboratory Simulation and Training Technology Center has entered into a cooperative agreement with the University of Central Florida to conduct research that includes a series of empirical evaluations of VW training through 2017. Ultimately, this body of research will result in empirically-driven recommendations for designers, developers, and decision-makers within the training systems acquisition community. This paper presents the findings from the initial field study focused on the effectiveness the VW training provided during a refresher room clearing battle drill event involving 64 reserve unit Soldiers. This Training Effectiveness Evaluation (TEE) compared the impact of traditional classroom training to VW training on performance outcomes, stress, and workload. The results reported from this inaugural TEE provide the foundation for future research.