In this study, we explore how preservice secondary science teachers articulated their agency and structural awareness within racist-nativist policy and schooling environments that limit emergent bilingual students' opportunities to learn science. Our praxis-oriented analysis led us to characterize novice teacher participants' discursive positionings within this structure-agency dialectic--that is, what it means to teach science well with emergent bilingual learners in the context of structural exclusions--as deficit, distancing, or discerning. We then discuss how these preservice teacher positionings were a function of tension management for working within the structure-agency dialectic. In our discussion, we refer to this phenomenon as praxis crisis, that is, the disjuncture between theory and practice that occurs as teachers negotiate the real and perceived constraints of their work. We consider how the concept of praxis crisis that emerged from our work can be a critical dialogic tool for transformative learning in science teacher education research and practice, and how a praxis-oriented methodological approach can support more expansive and nuanced understandings of teacher learning.