Goal-Based Scenarios (GBSs) provide a framework for the design of instruction—a framework in which the student plays a role within a simulation, acquiring knowledge and skills in the process of pursuing a meaningful goal within the simulation context. Sickle Cell Counselor, a computer program designed to teach museum visitors about sickle cell disease by placing them in the role of a genetic counselor, is the first step in our development of GBSs. While using Sickle Cell Counselor, a museum visitor advises couples about the difficult decision of whether or not to have children when there is a substantial genetic risk of the disease. To carry out this task, the visitor can perform simulated laboratory tests and ask questions of several experts via interactive video. In this article, we describe Sickle Cell Counselor in terms of the GBS framework, present a detailed example of interaction with the system, and discuss the results of three evaluation studies.