Creating educational software generally requires a great deal of computer expertise, and as a result, educators lacking such knowledge have largely been excluded from the design process. Recently, researchers have been designing tools for automating some aspects of building instructional applications. These tools typically aim for generality, resulting in interfaces with limited, generic styles. An alternative, appropriate for more complex, interactive software, is to provide tools with special purpose task models. A prototype authoring tool for interactive educational software, called Goal-Based Scenario Builder, is illustrated, and a mode of interaction called Guided Case Adaptation is described. Goal-Based Scenarios (GBS) provides an engaging task through which learners can master a set of target skills. This case-based approach to software design involves the user, and creates an interactive dialogue in which the program and designer collaboratively apply adaptations to a retrieved case. The Investigate and Decide GBS model is applied, and its five phases are outlined: problem, do, decide, communicate, and wrap-up. An example dialogue is presented. An early prototype of this tool was tested by graduate students in a first-year seminar in creating their own GBSs. An informal evaluation of the tool based on student reactions provided early indications that the tool makes prototyping easier, and that it supports a fairly wide range of applications within the limits set by the model. A table summarizes GBSs created in the prototype testing, and two figures illustrate the application. (Contains 15 references.) (MAS)