This monograph describes the development and use of a 3D visualization teaching-learning trajectory for elementary age learners. Using design research principles, the authors developed this trajectory using the NCTM recommendations and the Spatial Operational Capacity (SOC) theoretical framework to guide lesson development. The SOC framework utilizes actual 3D models, 2D and abstract representations of the actual models, and, a dynamic computer interface, the Geocadabra Construction Box, which integrates these representations dynamically in real time. The work begins with describing the...