Curricular coherence is an indication of the alignment of content ideas, the depth at which they are studied, and the sequencing of ideas within and across grade levels and has been identified as an important predictor of student performance. This study examined the contribution of inter-unit coherence on energy to the learning of this concept over time. The concept of energy was interwoven as a core disciplinary idea and as a cross-cutting theme in six different units in a reform-based middle school curriculum. The unit posttests of students from a national field test of the curriculum were analyzed using Structural Equation Modeling to identify ways in which ideas learned in some units supported the learning in other units. Results indicate that inter-unit coherence enabled students to develop a deeper understanding of energy by providing repeated exposure over years rather than weeks, enabling knowledge constructed in one unit to become the prior knowledge to be built upon in subsequent units, and offering a broader range of contexts in which students could apply their ideas than could be accomplished in stand-alone units.