The aspects of model-based reasoning serve as the Focal knowledge, skills and abilities (KSAs) of the design patterns. They highlight distinct aspects of model-based reasoning in a way that supports either focused tasks (building on one or a few design patterns) or more extensive investigations (building jointly on several design patterns). This chapter overviews the design-pattern perspective on assessing model-based reasoning, as a prelude to the next chapters that look more closely at each aspect. A table charts the correspondence between the aspects addressed in the design patterns and practices in the Next Generation Science Standards.