Procedures for the ex ante assessment of public policies are currently in vogue across the OECD. Their design is typically informed by an instrumentally rational model of problem solving, which assumes that knowledge is collected, evaluated and then trans-lated straightforwardly into 'better policies'. This model has, it seems, been little af-fected by more than three decades of academic research which has demonstrated thathe reality of every-day policy- making is far messier. This paper analyses whether the uptake of ex ante assessment of policies is nonetheless capable of providing new op-portunities for knowledge to inform processes of policy deliberation and learning. Drawing on an analysis of policy assessment procedures in three countries and the European Commission, it finds that there are several ways in which assessment knowl-edge is used in the policy process. Moreover, its argues that policy learning occurs de-spite, rather than because of the instrumental design of the new assessment proce-dures, which tends to act as a barrier to open deliberation and knowledge utilisation.