Energy is never created or destroyed—so the saying goes. Many students will memorize this statement, but few adhere to it when making sense of everyday phenomena (Chabalengula, Sanders, and Mumba 2012). After all, it seems that energy pops into and out of existence all the time. Hot drinks get cold, sparks seem to form from nowhere and then disappear, and the energy we get from food and fuel is exhausted. While the energy conservation principle is simply stated, it is far from a concrete idea. Developing a deep understanding of energy conservation requires many years of study and a rich evidence base. Thus, A Framework for K–12 Science Education (NRC 2012) and the Next Generation Science Standards (NGSS) (NGSS Lead States 2013) recommend that students are not formally introduced to the principle of energy conservation until they are in high school. To prepare for learning about conservation, students in the middle grades should gather evidence of how energy is transferred in a range of familiar phenomena. An evidence base that supports a deep understanding of energy conservation must help students recognize that any time energy seems to be missing from a system, it has either been transferred to another system or has been converted into a form of energy that is more difficult to detect.