Since their introduction by the Conservative government in 2013, primary school children in England have taken a mandated grammar, punctuation and spelling assessment, which places an emphasis on decontextualised, standardised English and the identification of traditional grammatical terminology. Despite some concise criticisms from educational linguists, there remains no detailed and critical investigation into the nature of the tests, their effects on test takers, and the policy initiatives which led up to their implementation. This article contributes to this gap in knowledge, using critical language testing as a methodological framework, and drawing on a bricolage of data sources such as political speeches, policy documents, test questions and interviews with teachers. I discuss how the tests work as de facto language policy, implemented as one arm of the government's 'core-knowledge' educational agenda, underpinned by a reductive conceptualisation of language and a problematic discourse of 'right/wrong' ways of speaking. I reveal how teachers talk about the 'power' of the tests, intimidating and coercing them into pedagogies they do not necessarily believe in or value, which ultimately position them as vehicles for the government's conservative and prescriptive language ideologies.