On the basis of studies on corporal punishment by parents, I suspect that this is probably quite effective for controlling chidren's behavior while you have them under your authority, but also that it's likely to make them more likely to resort to violence in their own lives.

So the studies find that corporal punishment has immediate benefits, but insert a disclaimer that there are bad effects in ways that are less obvious (and therefore easier to fudge). This is just what one would expect if the scientists doing the study aren't willing to outright lie but don't want to seem pro-corporal punishment.