Indeed Marie-Claire, good point. By 'unstructured', do you mean like drinking, drug dealing, and having unprotected sex? ;). The literature we looked at was mainly about the relationship with student learning, and while the results varied, they all pointed in the same positive direction. We're planning on looking at other social impacts, but there isn't much out there (one study on how it reduced teenage pregnancies I think). I know this wasn't quite your point but anyhow you're right, it all does come down to how time is used, whether in the classroom or outside.