I was my band's Drum Major when we competed in Magic Music Days!!!! And I was soooooo nervous about that performance... my parents actually went down to WDW that same week-- they didn't go as chaperones, but rather just enjoyed themselves while us band geeks did our thing together. We did meet up briefly so I could give my daddy the video camera so he could record our parade performance, but other than that, we saw each other very little. As for MMD, I LOVED it-- for a high school kid, it's a great opportunity to experience WDW with some of the best friends you'll ever have.... I went 10 years ago (this May, actually!), and I still consider that to be some of the best memories I can recall. (What can be more fun than chilling at WDW with 80 of your closest friends??).
Oh, and in case you're wondering (and just for old time's sake), I'd like to toss a little boast in here-- my teeny little band, from a po-dunk mountain town in WV, BEAT EVERY OTHER BAND IN OUR CLASS to win 1st place in that particular parade competition. Lemme tell ya, going up on that stage in MGM to get that MASSIVE trophy was one of the coolest things I've ever done!
On a more personal note, I can honestly say that I am SO glad my parents decided to go to WDW that week, even though it wasn't a "family vacation".... Barely two months later (right after I graduated HS), we lost my dad unexpectedly to a rare leukemia we didn't even know he had. The video he got of me leading MY band thru WDW (and bragging about his "little girl" the whole while) was one of the last "great" memories I have of him.
I hope you all have a great time watching your son's performance, and wish your son's band the BEST OF LUCK! Knock 'em dead!