Virtual reality (VR) and augmented reality (AR) are emerging technologies with a variety of potential benefits for sustainability education. Here, learning processes such as flow and presence seem to determine the learning experience. Therefore, this paper presents the results of a mixed-methods study investigating a VR- and AR-based learning application on biodiversity developed by greenpeace. A total of 156 students tested the application addressing the Amazon rainforest and rated its efficacy in terms of effects on knowledge, interest, and attitude. Pre- and post-questionnaires as well as focus groups were used to uncover within-subject effects. The study results revealed that flow and presence had a moderating effect on knowledge and that this effect is strongest in learners with little prior knowledge. Presence also showed a moderating effect on one of three attitude measures. In general, the learning application was able to increase knowledge and improve attitude in this sample. The focus groups also revealed that the students engaged with environmental topics even after the experience. They also formed ideas for more environmentally friendly behavioral change. Moreover, the students described the application as impressive, captivating, and realistic. It can be concluded that presence and flow are crucial processes for learning with VR and AR technologies.