We describe the development, design, implementation, and preliminary classroom results of an innovative curriculum, "Focus on Energy," that supports learning about energy in Grades 4-5. The curriculum is grounded in the concepts of science as practice, model-based reasoning, and learning progressions, and builds on students' pre-existing ideas and resources. We illustrate how students gradually develop the ability to track energy forms, transfers, and transformations in increasingly complex scenarios. We present evidence, using a quasi-experimental design, that students who completed the curriculum were significantly more adept at these skills than students in comparable classrooms who experienced their districts' existing energy-related physical science curricula. Important features of the curriculum include: the careful selection of a limited set of concepts chosen to provide a sound foundation for future learning; a consistent conceptual framework (the Energy Tracking Lens) within which the students have agency to build and refine a model of energy; engaging hands-on activities that steadily build in complexity; accessible and versatile semi-quantitative representations that support reasoning and communication; individual, small-group and large-group meaning-making; and training and support for the teachers.