Qualitative classroom data from video recordings and students' written work can play important roles in improving mathematics instruction. In order to take full advantage of these data sources, it is helpful to have a strong analytic lens to orient one's reflections on the data. One promising analytic lens is the National Research Council's five stands of mathematical proficiency framework. It prompts teachers to examine the extent to which their students have attained conceptual understanding, procedural fluency, strategic competence, adaptive reasoning, and productive dispositions. This article describes how a pair of prospective teachers used the five strands to analyze and reflect upon qualitative classroom data from a series of lessons they taught. The insights gained during the process can help others anticipate dynamics involved in using the five strands framework during practitioner research and reflection on classroom data.