This article describes an action research project in which a sixth-grade teacher engaged students in writing about their problem-solving efforts. The written mathematical work provided new artifacts for examining students' metacognitive and mathematical communication skills, prompting the teacher to make instructional changes to address students' needs. As students transition from elementary school to middle school mathematics, topics become increasingly complex and abstract. This transition requires students not only to use their declarative and procedural knowledge but also to communicate how they applied conceptual knowledge in their problem-solving methods. (Contains 3 figures.)