short answer: have students be successful and come back talking it up to others. The challenge is providing the guidance from beginning to be able to perform the audition music. If others are able to perform it and your students are not, something is missing. Someone said start with High School. I disagree. If you can get MS students involved and successful, they will strive to achieve. I have been in places that had many participants and I have been in places where they were intimidated. It just takes one being successful to "break" the glass. Don't make it all about making the band as much as personal improvement. But, they want to be successful.