Problem solving continues to be a major focus of K-12 mathematics education reform. This case study shows how a teacher's middle school mathematics instruction evolved from teaching problem solving as computation exercises to teaching how to select and implement combinations of problem solving strategies. The teacher's thinking about problem solving instruction also evolved to encompass different understandings about what a problem is, what problem solving means, and what teachers' and students' roles are in teaching and learning problem solving. The result of this evolution was that the teacher's instruction became more closely aligned with reform goals for problem solving. This finding suggests that reform efforts should incorporate strategies and support for teachers to revise and refine their own instruction through reflection and dialogue with colleagues as they try out approaches and activities in their classrooms for teaching problem solving. (Contains 1 table.)