Abstract: This dissertation investigates the formation of ethnic identity among Ecuadorian immigrant teenagers in Ciudad Lineal, a working-class neighborhood of Madrid, Spain. Ecuadorian immigration to Spain from 1998 to 2003 involves one of the largest and fastest diasporas that we have seen in recent years, and is a dramatic instance of how immigrant minorities can become marginalized in society along legal, racial, and economic lines. I illustrate this process in a concrete way by focusing on several groups of teenagers and giving an ethnographic account of their struggles to reconcile their hopes and ambitions for a better future with the political, economic, and social realities that they face as working-class (and often undocumented) immigrants. Based on 16 months of research, I examine the central role of academic success or failure for the Ecuadorian students' understanding that they share an ethnic identity that is distinct from their Spanish classmates. In turn, I bridge classroom observations with fieldwork among two social groups of Latino students in the neighborhood—the Evangelical Church and Latino gangs—in order to explore how discourses on ethnic identity become implicated in students' social relationships outside of the classroom. Together, these observations reveal how the conception that Ecuadorian students are different from their Spanish peers, which is often articulated by essentializing mutually exclusive cultural differences, emerges within the social and institutional relations that Ecuadorian teenagers have with their peers, families, Spanish educators, social workers, policy makers, and politicians. By taking account of the connections between immigration law, the Spanish labor market, the educational system and discourses of immigration and ethnic identity, this study complements previous studies on the academic achievement levels of minority student populations.