Would like to note something that's been made a point of in this thread.
Good manners and sharp social skills are generally developed in the home. Not in public school. I've found that even in any form of schooling, you get any and every type of kid. I can guarantee that most of us have seen several kids throughout grade school that we just think are weird, creepy, or just plain strange.
They don't learn that behavior in school.
I've seen classmates from years ago in college now that still act as awkward as they did back then. And some as stupid as ever, and some as annoying as ever, etc.
The only change in behavior I generally see is extroversion and introversion; some of the soft-spoken classmates are more outspoken and some have calmed down compared to their hyper middle school days. Other than that, I haven't really noticed any change in social skills (more witty remarks, more interesting, blah blah).
I have noticed that some of the former classmates that have jobs now are more confident, but that's probably more along the lines of independence and responsibility.