One area of concern common to all designers of interactive systems is pinpointing where the design fails for the first-time user and how to improve it. Many design methods are analytic--good at tearing apart problems but unable to synthesize improvements. In this paper I will describe research I have done using one method derived from Conversational Analysis which not only aids in analysis but also provides the necessary synthetic element. The paper discusses the method in detail and its integration with standard software prototyping techniques and usability studies. A detailed example drawn from a three year project which developed a cardio-vascular simulation for use in teaching biology illustrates the method. Finally, an informal confirmation of the learnability, practicality and universality of the method was made through several years of teaching it to programmers in user interface design classes.