In this study, researchers evaluated the usability of game environments for teaching and learning about mathematical functions. A 3-Dimensional multi-user computer game called as "Quest Atlantis" has been used, and an educational game about mathematical functions has been developed in parallel to the Quest Atlantis' technical and pedagogical structure. The pedagogical aspects of the game were based on three theories of learning: experience-based learning, inquiry-based learning, and portfolio-based learning. For evaluating the effectiveness of the environment, four learners participated in the implementation in a lab environment and researchers observed and interviewed them. This paper includes information about the design process of the game world, and evaluation of its implementation, and reflections of the researchers.