This paper examines the properties of instrumental variables (IV) applied to models with essential heterogeneity, that is, models where responses to interventions are heterogeneous and agents adopt treatments (participate in programs) with at least partial knowledge of their idiosyncratic...

There is a large empirical literature on policy measures targeted at children but surprisingly very little theoretical foundation to ground the debate on the optimality of the different instruments. In the present paper, we examine the merit of targeting children through two general policies,...