Well, my high school marching band has been around for 4 years now, and already we're a competing band. After attending some competitions, quite a few of us noticed how awesome other bands are in comparison to us.
From what I've heard, these other bands have a middle school/junior high program for marching band that lasts as long as the average school football season. It made me think, well I'm already going into music as my career, why don't I come back to my hometown after graduating to work at the middle school and start up a pep band? Good idea?

You cleary want to do this but it wont work as a full time career. If you find yourself in a decent paid job or as a housewife then go at this idea in full force. Otherwise think about your future first!

I like the idea you should try it out

It's a nice idea, but I wouldn't get too attached to it right away. If you go on to college and study music and other things, you might find something else you'd rather do than come back home and promote your old high school's band. It's pretty common to change your major/career/goals many many times throughout your life or even just throughout one year (take it from me!). Start writing down ideas like these and goals you might have for the future and expand upon them, while also being open to new ideas as you continue your education =)

I really like the idea you should try it out.If you go on to college and study music and other things, you might find something else you'd rather do than come back home and promote your old high school's band. It's pretty common to change your career many times throughout your life.