Recent research demonstrates that videogames enhance literacy, attention, reaction time, and higher-level thinking. Several scholars have suggested that massively multiplayer online games (MMOs) such as "Everquest" and "Second Life" have educational potential, but we have little data about what happens when such tools are introduced in the classroom. This paper reports findings from two MMO-based courses in the context of situated learning theory. The first course, focused on the ethnography of on-line games, used the game "Everquest" as a vehicle for teaching research methods to 36 students in an undergraduate communication course. The second course used the game "Second Life" to teach the fundamentals of video-game design and criticism. Synthesizing comments from student web logs with data collected from follow-up surveys, the paper highlights key findings and offers concrete suggestions for instructors contemplating the use of multiplayer games in their own courses. Recommending that potential virtual environments be selected on the basis of genre, accessibility, and extensibility, it is suggested that game-based assignments are most effective when they build bridges between the domain of the game world and an overlapping domain of professional practice.