This paper presents some results of research aimed at contributing to the development of a professional knowledge base for teachers of elementary mathematics methods courses, called here "teacher educators." We propose that a useful unit of analysis for this knowledge could be the tasks in which teacher-educators engage pre-service teachers, and that the tasks could be indexed by a system of nested categories of actions required in the tasks and the analytic tools for carrying them out. The paper develops the seed of such an indexing framework, based on analyses of tasks in two methods courses. We argue that this seed is robust enough to be expandable, in the sense that categories could be added to it without destroying the existing ones. An expanded index, accompanied by a bank of tasks, would facilitate the development of a unified discourse to bring together, represent, and communicate, the vast experience of teacher educators.