Tiered vocabulary is a pervasive concept in academic scholarship, education policy, and schools. It involves placing individual words into hierarchically arranged tiers, based on their apparent simplicity, sophistication, utility, and complexity, with these categorisations used to determine which words carry value in the classroom. In this article I conduct a genealogy of tiered vocabulary and argue that it is a raciolinguistic ideology which frames the language practices of racialised and working-class children as deficient and requiring modification. I trace the ideological roots of tiered vocabulary to European colonial representations of the purportedly limited vocabulary of Black African communities. I then examine how tiered vocabulary emerged as a concept in 1980s US academic knowledge production, based on experiments led by white academics on predominantly Black children from low-income homes. I show how tiered vocabulary is descendant from deficit, anti-Black thinking which characterised mainstream educational linguistics in the 1960s. I then focus on how it has become normalised in England’s education policy in the 2020s, as part of a flawed theory of change which deems that the acquisition of academic language is a tool for enabling social justice. Ultimately, I show how tiered vocabulary is a flawed theory of language which ties together race and class in producing discourses of linguistic deficiency, and legitimises language policing which undermines the education of marginalised children.