In this exploratory study we considered how one teacher's understanding of proportional reasoning related to his teaching. We used Epistemic Network Analysis to consider the teachers' knowledge organization and connections between knowledge resources as a way to make sense of his understanding. Then, we examined how his understanding was reflected in his teaching. From our analysis, we found key aspects of the teacher's proportional reasoning from two interviews related to his lesson. We concluded that this teacher's knowledge organization influenced his ability to teach lessons in coherent ways. This has implications for professional development. [For the complete proceedings, see ED583608.]