This research focuses on how members of the UK Parliament engaged with evidence in relation to the policy decision leading to the Selective Schools Expansion Fund, a policy designed to enable the existing 163 English grammar schools to apply for additional funds to expand their intake. Although a small case study, the narrow focus provides a fertile setting for analysis of the relationship between research evidence, parliamentary debates and policy decisions. The article provides contextual background in relation to the dominant political parties’ (Conservative and Labour) education policy manifesto statements and a discussion on the nature and understanding of evidence. Particular attention is given to how evidence can be used to support claims and the importance of justified warrants. Using NVivo software, we identified the thematic content of 11 parliamentary debates and analysed the findings using descriptive statistics, which we tested with a playful, carnivalesque extrapolation of the data. Argumentative analysis shows that within the debates a number of rhetorical tools are used to avoid empirical evidence, including the deployment of a ‘moral sidestep’ which discourse analysis reveals in this case to be the repeated communication that grammar schools are ‘good’. In this way, Ofsted ratings are conflated with moral goodness, leading to a disproportionate diversion of school funding in their favour. This case study exposes strengths and weaknesses of parliamentary debate, which might be relevant to educational researchers who focus on evidence-based policy and to the policy makers and other stakeholders who engage with the evidence such researchers offer.