Six Flags Great America wants individuals and bands to perform in the park, and they get discounted tickets. Six Flags also wants choral groups and marching bands for discounted tickets. They are so cheap to get their own entertainment that they want other people to do it for them.
So, not only are they going to get a bunch of people to come to the park (especially choral or marching bands - How many people are in a marching band? - 100), but they get free entertainment out of them.
"I've been staring at the world, waiting. All the trouble and all the pain we're facing. Too much light to be livin' in the dark. Why waste time? We only got one life. Together we can be the CHANGE. So go and let your heart burn bright"
With all the brochures I've come across while being in the band room in high school, they have been doing this for a long time. Not just at SFGAm, but they offer this at most if not all Six Flags parks. Most high schools aren't going to venture on out to Six Flags for the weekend, do a parade route, and call it their big trip. Most schools can't afford to do random trips like this over a weekend, and the bigger schools that could are already doing something bigger and better. It's just not gonna happen.
Choral groups is something I don't recall seeing though, but I don't see them having a successful set-up anywhere in the park to actually get an audience unless they just start setting up randomly in open areas, sing the national anthem, or take over the Karaoke stage by Farmers Market. Having a secluded performance would be a waste to park guests, as they could go get the same entertainment at the high school of the group performing, without paying $50 to get in.
Not a new idea, just probably marketing it a little better.