This paper illustrates the use of simulation-based performance assessment (PA) methodology in a recent study of eighth-grade students' understanding of physical science concepts. A set of four simulation-based PA tasks were iteratively developed to assess student understanding of an array of physical science concepts, including net force, acceleration, velocity, and inertia. Illustrative examples drawn from the administration of these simulation-based PA tasks to a sample of eighth-grade students (n = 74) highlight the potential of simulation-based tasks for revealing conceptual understanding of science concepts and for informing curriculum development within the context of design-based implementation research. The paper also describes a variety of challenges encountered over the course of the development, administration, and analysis of the PA data that may be informative for researchers and educators as they consider implementing simulation-based PAs.