Dr. Charles Kinzer of Teachers College will argue that the most powerful electronic learning environments, and those with the greatest fidelity to principles of effective instruction, begin with clear specificity of theoretical assumptions that guide the construction of content and user interfaces. He will also argue that assessment of learning by participants in these environments must take into account conceptual change processes as well as changes in content knowledge. These arguments will be presented through examples of an ongoing project that began with theoretical assumptions related to case-based instruction and situated cognition, will show how those assumptions resulted in a particular type of user interface, and will present assessment tools that are being used to assess both conceptual change and change in content knowledge by participants using the environment.