I examine the impact of age within grade on victimization in elementary school in 17 countries. Identification relies on the instrumental variables approach drawing on school entry age rules. The results indicate that children are harmed by being the youngest.

In any nonlinear “difference-in-differences” model with strictly monotonic transformation function, the treatment effect is the cross difference of the observed outcome minus the cross difference of the potential non-treatment outcome, which equals the incremental effect of the interaction...