Hi Sharon and welcome to the Disney Parks Moms Panel.
How wonderful that your daughter's High School band will be marching prior to the
Main Street Electrical Parade.
You can view a copy of the Guide Map for the Magic Kingdom Park (from January 2016) on the unofficial website www.allears.net (http://allears.net/tp/maps/magic-kingdom-map.pdf). The parade route is denoted by a red dotted line on the Guide Map itself.
The Main Street Electrical Parade typically starts in Town Square and ends in Frontierland but I would recommend that you double check this with a Cast Member once you arrive at the Magic Kingdom on the day, just to be sure.
There are many great places to watch the Main Street Electrical Parade from although if you want to watch
Celebrate The Magic and
Wishes nighttime spectacular afterwards, I would suggest that you plan to get a spot in the Castle hub area or on Main Street, U.S.A.
Finally, in terms of a meeting place for the band to return to once they have finished their march, I would recommend that you speak to their band leader(s) in order to arrange a suitable location.
Wishing you a magical trip filled with memories which will last a lifetime!
Emma