Across Western Europe, immigrant-origin minority youth often struggle to belong socially and to develop national self-identification. Yet, almost no research to-date has asked how these youth perceive the cultural contents of the national identity in their residence country—or rather, to what extent they perceive youth like them to (mis)fit the national identity. The present study addressed this research gap by centering schools as developmental contexts of evolving belonging and national self-identification and newly inquiring into minority youth’s perceptions of national (mis)fit as critical levers of their national identity development. Drawing on data from two annual waves of the Leuven-Children of Immigrants Longitudinal Study (Leuven-CILS), a sample of 942 Moroccan- and Turkish-origin youth (Mage-T1 = 14.98, SD = 1.22; 52% female) in 62 Belgian schools was used. Cross-lagged analysis combined repeated measures of school belonging and national self-identification with vignette measures of the perceived national fit of (imagined) culturally different peers. While school belonging and national self-identification were unrelated over time, earlier perceived national fit uniquely enabled more national self-identification one year later, over and above evolving school belonging. These findings suggest that experiencing belonging in school does not suffice for minority youth to develop national self-identification. Schools may, however, promote national identity development through redefining national identities to include cultural diversity—thereby signaling to minority youth that they can fit the national identity.