I am currently playing a piece called Eventide by Matt Conaway that might be my favorite piece of my career. Very, very playable, and very moving. Highly recommend it!
Other pieces to check out for that age group IMHO: Ghosts in the Graveyard by Scott Watson (fun novelty, but you need an ooga horn. My wife and I built our own for less than $30), March from 1st Suite for Military Band – Holst (arr. by Michael Story), Most easy RW Smith pieces are great for this level (Sound and the Fury, Serengeti Dreams, Furioso, Jupiter [arranged w/ Michael Story] etc.). I did James Swearingen’s “Song for Peace” for my winter concert, which is very pretty. Defeating the Giant by Rob Grice was a favorite of my band (His music is also EXCELLENT for this level). Plaza De Toros by Michael Story is excellent. I liked Rhythms of Rincon (but I think it’s out of print).
I could go on and on. Hope this helps! I’d love to hear what your program is when you finalize it!