To test the concept of multiuser 3D virtual environments as media to teach semester-long courses, we developed a software prototype called Aeroquest. An aerospace design course--offered to 135 second-year students for university credits in Fall 2009--was divided into two groups: the real-world group attending lectures, physically, in a campus hall and the virtual-world group attending lectures, remotely, in Aeroquest. To date, numerous studies on the educational use of multiuser virtual environments have been reported in the literature. However, among studies on virtual-world-based courses, our investigation was one of the firsts to employ learning outcomes (rather than affective states) that were objectively measured (rather than subjectively reported) against a control group. We found that the virtual-world group achieved the performance benchmark, defined by the exam score of the real-world group, within a 95% confidence interval, suggesting the virtual worlds' untapped potential as a teaching platform in early engineering courses--especially for distance education. (Contains 2 tables and 4 figures.)