Promoting critical science agency (CSA) may be one way to promote educational justice. CSA is using science with other powerful forms of knowledge to address issues of injustice. However, the process of enacting CSA is always embedded within a sociopolitical context, which positions some students with more power than others. Drawing upon a social practice theory analytical lens with a focus on power and using critical participatory ethnography methods, this study investigated the ways middle school students restructured power hierarchies as they worked to complete the design challenge of making their classroom community more sustainable, and how power hierarchy restructuring impacted students' opportunities to enact CSA. Findings show as the students enacted collective CSA, they were responding to unmet students' needs grounded in systems of power operating within their classroom. Throughout the engineering design process, students' understandings of their defined issue of injustice was both refined and critical to their technical and social design considerations. Finally, as the groups enacted CSA, power hierarchy disruptions, though incomplete, through the recognition of students' expertize and distributing roles, supported their efforts to address their class-wide concerns. These findings highlight how restructuring power hierarchies supported youth enacting collective CSA, which then further supported them in reshaping their classroom community to be more justice-oriented.