A scaffolded metacognition activity was incorporated into the laboratory component of the introductory physics course at Western Washington University (WWU) and Whatcom Community College (WCC). Each week, students wrote reflectively to contrast their initial and current understanding of a specific physics topic, and described the "trigger" events that led them to change their thinking. Goals were to enhance conceptual understanding as well as the depth and quality of student reflection. A coding scheme was developed to evaluate student reflections. We present the scaffolded activity and coding scheme, as well as preliminary findings about changes in student reflection over time and correlations between amount of reflection and conceptual learning.