Public Education Rambling

I have one question: Why can't we just leave some kids behind? The public education system in the US is so screwed up, the entire thing is ridiculous. We waste so much money trying to teach people that are literally unteachable, that the people with intelligence and potential get left behind and forgotten.
Another problem I have with the public education system is the total lack of discipline. Kids can literally get away with whatever they want to, and receive nothing but a slap on the wrist, if that. I propose we stop worrying about being "politically correct" or hurting anyone's feelings, and bring back the old-fashioned public embarrassment method.
I recently heard a story from one of my father's friends, now in his late 40's, from when he was in the 4th grade. He attended a private catholic school, and was required to wear a uniform, part of this being a belt. Once when he left his belt at home, he was sent to the principal's office, where they sent him back to class wearing a pink ribbon in the place of his belt. This apparently worked, since he never forgot his belt again, and I think this is a good lesson for everyone.
If the public schools these days would actually implement a policy of real punishment instead of the slap-on-the-wrist techniques that do nothing, then things might actually improve. But parents are so worried about people making their children "feel bad" or "getting embarrassed" that they won't have any of it, and wonder why the public school system is going down the toilet. Back in the days of the paddle, things actually got done, and you didn't talk back to the principal.
An incident at my high school last year happened that shocked me beyond belief. There was a fight in the cafeteria, and one student actually punched an assistant principal in the face. I think this is totally unacceptable and out of control. That student should have gone to jail, but instead he went to juvi for a couple days, and after that he was back in school. What would you do if you were in charge?