We stayed at ASMo in January. At the end of our trip the cheerleaders were starting to move in. I really didn't notice them that much, except like others posting, they were practicing their cheers in the courtyard area. (Out of the way, not a big deal.)
They were getting to be a pain in the parks though. The lines were reasonable, until you get a group of around 15 - 20 in front of you.
And being teens out together, they can get rowdy, but not out of hand. Actually they are better than the bickering families we sometimes get around.
In May, we were at WDW when bands were there. The only bad thing we noticed was all the young (and even pre) teens together without adult supervision of any kind in the parks. And the kids acted like it too. They were rude, pushy, loud, obnoxious, and generally took over what area they happened to be in.
I was surprised at how many were just turned loose with no one to watch them. I think they should have an adult with them, even for their own protection.
And I don't know that what we saw were just band kids, but judging by the same t-shirts they all were.