This study investigated the affordances and constraints of a VR-based learning environment for the teaching training of university graduate teaching assistants in relation to the task, goal-based scenarios, and learning support design. Seventeen graduate teaching assistants participated in a multiple-case study with an OpenSimulator-supported, simulation-based teaching training program. The study indicated that the VR-based learning environment fostered participants' performance of interactive teaching and demonstrative instruction, while training them to notice and attend to students' actions/reactions during the instruction. On the other hand, there is a competition between physical reality and functional intelligence in the VR environment. We propose the integration of experience, affordance, and learner analyses in planning and designing a VR-supported learning intervention.