This study analyzes discussions from online language teacher education to understand how conversations between monolingual and bilingual preservice teachers (PSTs) in the US create and delimit structural constraints on teachers’ agency, (re)positioning teachers’ capacity to act in the instruction of emergent bilingual students (EBs). Employing positioning theory within a critical discursive psychology approach, findings demonstrate how bilingual PSTs pushed back on structural constraints introduced as potential barriers to achieving linguistic pluralism in monolingual teachers’ posts, asserting teachers’ agency by simultaneously positioning themselves and others as capable and responsible for education of EBs. These findings inform theoretical understandings of agency as a discursive construct and offer insights for teacher educators as they conceptualize the role of discursive exchanges in developing PSTs’ understanding of structures and agentive possibilities regarding the equitable education of EBs.