Teaching socio-scientific issues (SSIs) allows students to explore science ideas and practices intertwined with complex social phenomena, which can promote significant growth in critical thinking. Sadler, Barab, and Scott (2007) suggested specific critical thinking competencies associated with the negotiation of SSIs that capture the complexities of what students can learn through participation in SSI learning opportunities. The authors refer to these competencies collectively as socio-scientific reasoning. They are: (1) Examining the social and scientific complexity of an SSI; (2) Analyzing diverse perspectives held by multiple stakeholders; (3) Examining specific areas of further inquiry; (4) Skeptically evaluating scientific findings and media messages about science; and (5) Recognizing both the affordances and limitations of science for understanding and solving complex SSIs. Teachers may mention current science events during a related lesson, but the most effective issues-based teaching requires a more thorough approach. They believe SSI can be the central context through which the core ideas of science, practices, and crosscutting concepts are explored. The authors developed the Rigorous Investigation of Relevant Issues [RI][superscript 2] teaching and learning framework as a systematic approach to SSI instruction (Sadler, Foulk, and Friedrichsen 2017). The [RI][superscript 2] framework encompasses lesson plans, presentations, and student activities. In this article, they present an overview of an ecology unit for high school learners developed with the [RI][superscript 2] framework and then highlight ways in which the learning of SSR, as an important aspect of critical thinking, was supported through the unit. This ecology unit, titled "The Karst Connection," evolved through 17 years of instruction by the lead author, and in 2015 was redesigned around the [RI][superscript 2] framework (Kinslow and Sadler, 2017).