This paper aims to map and understand tactics and practices of resistance to standardised testing in England by focusing on the "More Than a Score" (MTAS) campaign. More specifically, this paper examines the role of professional organisations affiliated to the MTAS campaign in the production and mobilisation of expert knowledge as a tool for resistance. In particular, by examining their transactions and exchanges, we identify three main tactics of resistance: i) a diffused policy approach, ii) expert reports, and iii) a deep understanding of network boundaries. The development and use of these tactics allowed MTAS to move beyond traditional forms of resistance, towards more complex and granular modes of refusal and contestation. We conclude with a discussion about how this work can extend our understanding of resistance and the tensions and compromise that multi-stakeholder resistance involve.