Making informed decisions about socio-scientific issues requires socio-scientific reasoning, which is highly challenging for students. This construct has four dimensions, including recognizing complexity, analyzing multiple perspectives, appreciating the need for ongoing inquiry, and employing skepticism. To support its development, we integrated established principles for designing socio-scientific issues learning environments with the Knowledge Community of Inquiry model. A design-based research study was conducted with two iterations, involving 85 eighth graders, to examine the effectiveness of the integrative approach in supporting students’ socio-scientific reasoning and decision-making. The web-based unit “Asthma in the Community” was adapted and enacted with the students. In the first iteration, the socio-scientific approach was applied, and in the second iteration, the unit was redesigned with features from the Knowledge Community of Inquiry approach. Results showed that all students who participated in the second iteration developed socio-scientific reasoning, made better evidence-based decisions than those in the first iteration, and expressed an understanding of decision-making processes in a community, which is suggested as new, fifth dimension of socio-scientific reasoning. This fifth dimension is suggested as essential for coping with decision-making in socio-scientific issues in the networked society, and the study suggests how to design learning environments that can support its development.