This paper summarizes the pedagogical design, product development and empirical evaluations of the game series, Animal Class, in terms of design study. The design phases, as well as the evaluation phases (N=2718), were carried out between the years of 2005-2007. The pedagogical idea of Animal Class is to place a learner in the role of teacher in a virtual world. The game encourages a learner to think reflectively, leading, in a best case scenario, to conceptual changes in the learner's mental conceptual structure. The evaluation phase showed that the main strengths of these learning-by-teaching types of games are good learning outcomes and positive user experiences. (Contains 7 figures and 3 tables.)