The development of learning environments based on full-body interaction has become an increasingly important field of research in recent years. However, the design and evaluation strategies currently used present some significant limitations. Two major shortcomings are: the inadequate involvement of children in the design process and a lack of research into what meanings children construct within these learning environments. To tackle these shortcomings we present an evaluation-driven design approach, which aims at analyzing situated interpretations made by children. These interpretations are then used to guide and optimize design in an iterative process of design and assessment. This evaluation-driven design method was applied in the development of the EcoSystem Project, a full-body interaction learning environment for children aimed at supporting learning about environmental relationships. The application of this iterative approach proved to be highly effective both in facilitating continuous improvements in the proposed design and in reducing misconceptions by children using the environment. Moreover, experimental evaluation reported significant learning gains in children. This suggests both the potential of using full-body interaction to support learning and the effectiveness of our evaluation-driven approach in optimizing design solutions through the analysis of children's interpretations.