I am not saying that the karate school should be the sole source of discipline (far from it)
Organized sports have been advertising based on "character building" for a long time, long before the martial arts industry picked up that line and ran with it. And sports do build some good traits, leadership, teamwork, fair play, perseverance, etc.
But they are side effects, not primary goals. Putting a child in a activity they don't want to do to teach them "discipline" is the kind of reasoning that probably led to having a undisciplined child in the first place.
For martial arts, or any activity, to have a positive effect on a person it has to be something they want to do.
As martial artists, and some of us instructors I think it is important to remember the side-effects of what we do, which include "character development" if done right. But it seems that there are a lot of schools that go on and on about discipline and character, yet have no idea where those things come from in relation to the martial arts. Instead they seem to think it's about sharp stances, bowing, screaming "yes sir" and winning trophies for looking like a little soldier on pajama parade.
It might feel like your teaching those things, but your not. It's load, in your face, and feels like its working, but it's more like going on a bacon and ice cream diet to get healthy. Even if you lose weight, your in worse condition then when you started.