This case study looks at the effectiveness of policy instruments aimed at reducing the number of underperforming primary schools in a system with a long tradition of school autonomy. It reviews relevant Dutch policy developments in education since 1998 and provides an in-depth analysis of five selected schools and their responsiveness to the policy instruments under study. Interviews with relevant stakeholders explore a key issue: what happens after a reform is introduced, and what are the elements that make it successful (or not)? The study suggests that there is not a linear cause and effect driving changes in educational performance of schools. For example, even the assignment of the label ‘very weak’ can elicit a positive response from one school and a negative response from another, depending on the local context, history and staffing situation at the school. The same intervention can thus create a vicious cycle that triggers increasing deterioration of schools or a virtuous cycle that improves conditions to an extent that surpasses the original goal of the reform. This goes some way to explaining why some reform measures unintentionally backfire while others quickly (‘virally’) spread over the system and set a virtuous cycle in motion that engages all parts of the system.