Eastern martial arts schools often tout that children will learn "discipline" by attending their classes. Perhaps this is true -- expecting a commitment to a training regiment and the following of the school rules, along with an enforcement of consequences for breaking those rules, with male "role models" in the school to provide guidance -- it is possible that a martial arts school can have this salutary effect.
But there is something to be said for males (in their teens and beyond) to have a controlled exposure to the reality of violence and taking a punch (to the face or elsewhere), as Vox Day points out. This will encourage self-understanding, necessary for "self-mastery" with regards to dealing with anger and the use of violence, when today many harbor dangerous fantasies about their capabilities in a fight. Might it be that the benefit of discipline is not really possible until this basic self-understanding has been achieved?