The ‘Revised Prevent Duty Guidance for England and Wales’ presents statutory guidance under section 29 of the Counter-Terrorism and Security Act 2015. This guidance states that ‘Schools should be safe spaces in which children and young people can understand and discuss sensitive topics, including terrorism and the extremist ideas that are part of terrorist ideology, and learn how to challenge these ideas. The Prevent Duty is not intended to limit discussion of these issues’. The Prevent Duty also requires schools to identify pupils at risk of radicalisation and have in place ‘robust safeguarding policies’. Schools that are unable to satisfy Office for Standards in Education will be subject to ‘intervention’ (maintained schools) or ‘termination of funding’ (academies and free schools). This article explores the interplay between the statutory requirement to provide opportunity for pupils to debate and explore issues relating to citizenship in the public sphere in the light of religious and political discourses and the statutory requirement to monitor and report potential ‘vulnerable’ pupils. It asks what measures are employed to judge ‘vulnerability’ and ‘risk’ when they are encouraged to promote debate and active political engagement. The article argues that in discharging their Prevent Duty, teachers become self-regulating, ‘governmentable subjects’ themselves.