In the Maine Physical Sciences Partnership (MainePSP), we have observed that students improve the way they analyze thermal energy after instruction. Still, many of them continue to use the idea that "coldness" transfers. Past researchers have identified that "cold" is commonly perceived as a separate heat energy. Nevertheless, we have not found specific activities to address this idea. We present analysis of students' conceptual understanding of energy transfer and how the use of coldness as an

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... entity plays a role in it. We explore how both ideas interact with each other using two different multiple choice items. To illustrate the difficulty of addressing student difficulties with coldness, we analyze a collaborative session among K-12 teachers who modeled energy transfers in scenarios similar to the student items and had to work to reconcile the conflict between the two models. Our study shows how the concept of coldness as an energy entity can co-exist and be in conflict with the idea of thermal energy, even after instruction. edited by Jones, Ding, and Traxler; Peer-reviewed,