Hi Danielle!
Welcome to the Disney Parks Moms Panel! First off, a super huge double ear cheers to your son's school in being able to march at Walt Disney World Resort! My three-year-old love love loves to clap along and wave to the pre-parade bands. I think he thinks these students are Disney royalty too!
I've only ever seen the Disney Youth Programs
Performing Arts performances at either the stage at Disney Springs (which is usually choral or dance routines) or in
Magic Kingdom Park. There are a few classes that take place in Epcot, but
instrumental groups 99 percent always perform in Magic Kingdom. My son loves the daily "3 O'clock Parade"
Festival of Fantasy Parade, so much so that we usually camp out an hour to 90 minutes in advance to get the best seats. A few trips ago we saw three different bands in the hour leading up to the parade, but it's possible that your group might have a morning or evening schedule. The route traveled starts between Adventureland and Frontier Land, goes east towards Cinderella Castle, makes a 10 to 6 clockwise rotation around the hub in front of the Castle, and then heads down Main Street USA. For perfect head-on picture taking, get viewing spots near the Partners Statue facing Liberty Square.
These kids are going to have the trip of a lifetime, with memories that will last forever. Definitely search through the questions that have already been answered here on the Disney Parks Moms Panel to get ideas of how other school groups have traveled to Walt Disney World.
I hope this helped, Danielle!
~Kristen