There is little principled empirical work to support the educational effectiveness of virtual reality (VR) because it is a new and fairly inaccessible medium. The purpose of the studies described in this paper is to evaluate the effectiveness of a virtual environment, specifically an immersive virtual reality environment, as a learning medium in domains with a high conceptual and social content. The learning environment used is called NICE (Narrative-based, Immersive, Constructionist/Collaborative Environments), an immersive participatory virtual world for young users based on a constructivist approach to education, on collaborative learning, and on narrative development. NICE is designed to encourage exploration and experiential learning by utilizing the strengths of virtual reality: a combination of immersion, direct engagement, immediate visual feedback, and interactivity.