This chapter explores the intersection between language teacher agency, language ideologies, and transpositioning in the context of heritage language education. Transpositioning is an adaptation of the concept of positioning in social psychology and is defined as the process by which individuals articulate their personhood by adopting changeable identities in interaction. Specifically, the chapter focuses on three teachers from different sociolinguistic backgrounds teaching Spanish as a heritage language in a U.S. university. At the core of the chapter is the original proposal of critical (re)actions in relation to transpositioning. Critical (re)actions are defined herein as the spontaneous seizing of a seemingly unimportant moment to create a meaningful learning opportunity grounded in embodied, situated knowledge and response-ability. In this context, critical (re)actions are small but transformative moves teachers can make to agentively resist monolingual and deficit-framed ideologies and open new opportunities for growth. They are evidence of critical teacher agency. To ground a comprehensive definition of critical (re)actions in relation to transpositioning, the chapter presents three vignettes collected by means of ethnographic observations and individual interviews and engaged with through a combination of phenomenological and multimodal conversation analysis.