The collection of which this article is a part is entitled "Functions of Assessment in Teacher Education." The other papers in this set draw our attention to multiple functions of assessment including peer evaluation, promoting reflection, use of technology in demonstrating teacher competence, and validating new national standards of excellence among veteran teachers. Our contribution to the conversation is a modest one--a simple heuristic device that we have found useful in designing and administering assessments in teacher education programs in the USA. Our purpose is to give a brief description of the heuristic device and the assumptions that support it and then to illustrate how we have made use of it in our work as teacher educators.