3D multi-user virtual environments (MUVEs) are considered a technological advancement that, in the coming years, will have a significant impact on how students learn. On the other hand, the factors that shape the learning experience in such applications are not well studied. This chapter is an attempt to fill that gap. It reports the development and validation of a scale to measure the factors that come into play when primary school students use MUVEs in formal educational settings. Perceived learning effectiveness, perceived ease of use, presence, motivation, perceived application realism, interactions, enjoyment, as well as collaboration were used to develop a questionnaire that initially included 34 items. A total of 352 sixth-grade primary school students used a MUVE in formal educational settings and the aforementioned questionnaire was administered to them. The exploratory and confirmatory factor analysis revealed the existence of 7 factors and 24 items that were retained in the final version of the scale. The factor structure of the questionnaire is also discussed.