We investigated whether it is possible for 12-year-old students to develop a qualitative conceptualization of energy and four associate features (forms of energy, transfer processes, conservation, and degradation) as a framework for constructing interpretive accounts for the operation of physical phenomena (specifically, for changes taking place in simple physical systems). We implemented, in authentic classroom environments, a specific teaching-learning sequence designed to promote this particular learning objective. The implementation involved three intact classes (N?=?64) and lasted nine 80-minute sessions. We collected data through open-ended tasks and follow-up interviews, so as to investigate what could be achieved by students in terms of employing energy for analyzing the operation of physical systems. The findings suggest that, to a large extent, the students were able to productively meet this challenge. At the same time, the data revealed specific conceptual, reasoning, or other difficulties they encountered. Our findings have implications for specific issues debated in the literature on teaching and learning about energy, including the developmental appropriateness of energy as a learning objective for the lower middle school grades and the instructional value of forms of energy. We discuss boundary conditions in terms of what falls within the reach of lower middle school students and highlight implications for the characteristics of physical systems that could be productively analyzed by students of this age.