Governments in the advanced industrial countries increasingly rely on supply-side reforms to intervene in the economy. This article examines one such reform, that of vocational education and training in France, whose successful implementation required that private actors cooperate not with the state, but with each other. As demonstrated through an empirical analysis of two employment zones, theories of institutional design that underscore the necessity of sanctioning cannot explain the successful emergence of cooperation, because new sanctioning regimes lack credibility under the uncertain conditions of economic reform. The primary obstacle to successful implementation of these reforms is uncertainty about the consequences of reciprocal cooperation, and the article highlights the mutual roles of states and employers' associations in overcoming this uncertainty. Active collaboration between policymakers and employers' associations, which have uniquely good access to private information about firms, is necessary to enable state policies to target those firms which are the most likely potential cooperators.