This paper uses a Critical Race Theory perspective to explain the everyday racisms -- racial microaggressions -- directed towards students of African and Caribbean descent during a non-statutory Black History unit, at an English secondary school. Applying a racial microaggressions framework to ethnographic data, this paper finds that experiences of studying Black History by students of African and Caribbean descent are dominated by various types of racial microaggressions including: micro-invalidation, micro-insults and micro-assaults. These experiences are symptomatic of wider racist structures and processes within the National Curriculum for History, based upon the ideology of white supremacy. This paper concludes that the racial microaggressions framework allows for useful ways of thinking about the function and purpose of Black History Month and Black History in schools, and its opportunities for exposing wider institutional and ideological underpinnings that legitimate deficit understandings about black people in school classrooms.