We describe the development and validation of the Quantitative Assessment of Socio‐scientific Reasoning (QuASSR) in a college context. The QuASSR contains 10 polytomous, two‐tiered items crossed between two scenarios, and is based on theory suggesting a four‐pronged structure for SSR (complexity, perspective taking, inquiry, and skepticism). In the context of pre‐post measurement within a 1‐week SSI‐based unit on fracking, we found that the four sub‐constructs represent a one‐dimensional progression of ideas, and that SSR is largely independent of declarative knowledge. In the validation process, we discovered small inconsistencies in item functioning between scenarios in the areas of complexity and perspective‐taking, but determined that resulting biases sat well within the uncertainty in students’ measures. In light of future development and use of the QuASSR, we determined that use of a single scenario is sufficient to produce a measurement reliability of 0.7. Given the time it takes for students to complete a scenario, we consider a 3‐scenario QuASSR, and its accompanying measurement precision of 0.85, to be the practical upper precision limit of the QuASSR when used in experimental contexts. Finally, we found no significant change in SSR due to the SSI‐based intervention. This mirrors prior reports of short‐duration interventions targeting SSR. Our data suggest that as a cognitive construct underpinned by political, moral, and ethical ideologies around SSI, successful efforts to facilitate growth must target SSR as a central focus upon which more basic content knowledge is contextualized, so that sufficient instructional duration can be given to this important construct. © 2016 Wiley Periodicals, Inc. J Res Sci Teach 54: 274–295, 2017