Science standards of different countries introduced disciplinary core ideas and crosscutting concepts--such as energy--to help students develop a more interconnected science understanding. As previous research has mostly addressed energy learning in specific disciplinary contexts, this study targets students' cross-disciplinary understanding of energy. Since no respective test instrument was available, we present the development and validation of an instrument that can be used to compare students' progressing energy understanding across contexts from biology, chemistry, and physics. In a cross-sectional study, we administered the new instrument to N = 752 students at the end of grades 6, 8, and 10. In addition to a detailed discussion of the instrument's reliability and validity, the study findings compare progressing energy understanding in the three disciplinary contexts. With regard to energy as a crosscutting concept, the results are then used to discuss how students' energy understanding may be connected across disciplinary boundaries.