The following chapter provides a critical analysis of the introduction and development of racial classifications in secondary schools of the Romanian Kingdom and the Hungarian region of Transylvania during the late nineteenth and early twentieth centuries. In doing so, it traces, on the one hand, the legacies of Johann Friedrich Blumenbach’s racial classifications within the broader scientific circles and its further ontological conceptualization as a theory of domination and assimilation of minoritized communities. The chapter further looks at how the development of race science in Romania shifted from theorizing to racially measuring the local Romani and Sudanese ethnic communities. On the other hand, it analyzes the ways in which racial classifications were adopted within the teachings of natural history in secondary schools and how several methodological changes contributed to the legitimization of racial discrimination. The chapter argues that secondary schools, along with other state scientific institutions, are crucial spaces for transforming social realities, shaping in this way a nationalist, anthropocentric and racial hierarchical thinking, while legitimizing at the same time both the domination of minoritized groups and non-human species.