This paper addresses the impact of teachers' beliefs about argumentation and their community of practice framed views of teaching on co-designing an environmental health afterschool club curriculum with researchers. Our team collaborated with a group of four middle school teachers, asking them to co-design a club that would facilitate (1) students' understanding of environmental health, (2) use of electronic resources, and (3) argumentation skills. The process included researcher-led sessions emphasizing the importance of argumentation to science and teacher-led curriculum design sessions. The qualitative analysis of the meetings and teacher interview transcripts suggests that while teachers viewed argumentation as important, its practice was relegated to the background by the focus on student engagement and perceived logistical and systemic constraints. The paper concludes that in addition to stressing relevance of argumentation to science learning, researchers involved in co-design need to emphasize the potential of argumentation to engage students and to fit into science curriculum. The analysis also reveals teacher--participants' views of environmental health as an important area of middle school education, relevant to students' lives, linkable to the existing curriculum, essential for informed citizenship, and capable of inspiring interest in science. These findings underscore the importance of integrating environmental health into science education and advocating for its inclusion in informal and formal educational settings.