Socio-scientific reasoning (SSR) is key to helping students take informed positions around socio-scientific issues (SSI). SSR comprises four competencies: recognising complexity of SSI's, multiple perspectives around SSI's, the need for ongoing inquiry around SSI's, and skepticism around different parties' claims made about SSI's. The Quantitative Assessment of SSR (QuASSR) provides a promising measurement framework, but there are still important questions around the ability of this instrument to measure transfer across different scenarios and change in SSR over an intervention. Further, prior work suggests that the four competencies may constitute a progression. We explored the ability of the QuASSR to measure transfer of SSR across three different SSI's using 2-faceted and multi-faceted Rasch models. We used path analysis to test the hypothesis that competencies associated with SSR formed a progression. We found transfer or neartransfer of SSR across the three scenarios, and that the competencies comprise a unidimensional hierarchy. Perspective-taking is a necessary bridge between students' understanding of complexity and the higher-level competencies of inquiry and skepticism. Inquiry and skepticism were found to be conditionally independent upon accounting for perspective-taking, supporting the idea that seeing multiple perspectives around SSI's is central to development of the other SSR competencies.