Latino students’ educational success is central to America’s prosperity—in traditional immigrant destinations and in New Latino Diaspora locations, previously unfamiliar with Latinos. Implicated in this success is the reception young immigrants receive, especially the ways in which they are identified in schools. We describe findings from 6 years of ethnographic research in a high school and an elementary school in the New Latino Diaspora and describe divergent ideologies of Mexican-immigrant Spanish circulating in each context. We show how monoglossic language ideologies in the 2 schools frame teenage immigrants as deficient and younger immigrant children as proficient. These ideologies influence both elementary and high school decisions about how to serve immigrant students, and they shape students’ own language practices, which have implications for their learning opportunities and future trajectories. We argue that attention to these divergent language ideologies is necessary for understanding different educational outcomes across decimal generations of immigrant students.