This article reports and analyzes different types of problems that nine students in a Master's Program in Mathematics Education posed during a course on problem solving. What opportunities (affordances) can a dynamic geometry system (GeoGebra) offer to allow in-service and in-training teachers to formulate and solve problems, and what type of heuristics and strategies do they exhibit during this process? Results show that combining semi-structured problems with the use of GeoGebra can be useful in motivating and involving teachers in various episodes of problem formulation. In this context, important strategies included analyses of the variation in the attributes of figures using dynamic points and loci. [For complete proceedings, see ED581294.]