Whereas most collaboration-based innovation policies aim at fostering efficient ecosystems of innovation, evaluations of the behavioural impact of such policies remain few and far between. Relying on external-to-the-policy network data to build a counterfactual approach, this paper addresses three main evaluation issues: do cluster policies make firms more collaborative? Do they encourage local ties? Do they induce network additionality? Focusing on French data, our results suggest that cluster policies may lack effectiveness in tackling network failures.