Make a big deal of the kids who do. We have a perpetual plaque on the wall that gets updated every year. I've seen schools do a big banner with all the kids' names. Put it all over the social media, get the campus/district social media involved.

Make the trip really fun. On the first day we check the kids out from school earlier than is really necessary, and stop for a fast-food meal on the way to the rehearsal. On the 2nd day we do a nice sit-down meal somewhere. Doesn't have to be fancy, last year I think was Chili's, but something a step above what they get at a normal band function. This is all paid from band funds.

The best pitch I ever heard for Region band is "imagine a band where all of the players are really good at their instrument, and they call care about being the best they can be." The kids who want that environment will rise to the top.