Our field often assumes mechanistic reasoning is inherently valuable. Underlying this assumption are two justifications. First, mechanistic reasoning is inherently good because it resembles the way scientists reason about the physical and natural world. Second, it is good irrespective of what scientists do because it is a productive way to construct or interpret knowledge about the world around us. The latter argument echoes claims elsewhere that science education prepares students to reason about science in their everyday lives. In this work, we unpack this tacit assumption about the value of mechanistic reasoning in school science. Specifically, we question the justification that mechanistic reasoning as it appears in-school prepares learners for mechanistic reasoning in-life. To do so, we juxtapose mechanistic reasoning emphasized in a school activity contextualized by the Flint water crisis with mechanistic reasoning used by Flint residents to prompt civic action. We find that the school activity authorized mechanistic reasoning only insofar as the mechanism students produced used “right” components to achieve a “right” answer determined by the teacher. Learning about content was the focus of school mechanistic reasoning. By contrast, Flint residents critiqued, constructed, and refined mechanisms until those with power took meaningful action to reduce toxins flowing through the city. How (or whether) a mechanism mapped onto what a professional scientist might construct was not “the point” of such reasoning. Here we call on our community to consider how we might make mechanistic reasoning in school better resemble the unbounded, complex, and community-driven mechanistic reasoning in life.