Among the many responsibilities of K-12 educators is to promote the development of environmental literacy among their students. Contentious environmental issues are often considered socioscientific issues (SSI; e.g., climate change) in that they are rooted in science, but a myriad of non-scientific (e.g., cultural, political, economic, etc.) factors must be addressed if those issues are to be successfully resolved. Teachers often report being ill-equipped to address these non-scientific factors, which may be due to struggles with employing socioscientific reasoning (SSR). SSR includes understanding the complexity of SSI, engaging in perspective-taking and ongoing inquiry about SSI, employing skepticism when dealing with potentially biased information concerning SSI, and recognizing the affordances of science and non-science considerations in resolving those issues. In this study, mathematics and science teachers who engaged in an SSI-oriented professional development demonstrated a range of sophistication across the dimensions of SSR, with science teachers tending to exhibit more sophistication in their SSR than mathematics teachers. Herein, we share and discuss the results of the study, including the prompts and scoring rubrics with exemplars, which can be used to prepare teachers to teach about contentious SSI and enable them to more effectively instruct and evaluate their students when doing so.