Your high school student comes to you and tells you they want to go to music school. You like the kid well enough, but you aren't convinced they have what it takes to study music at the college level. It's a delicate situation; you don't want to scar them for life, but you also don't want to set them up for humiliation but letting them think they're prepared for auditions when they aren't. What do you do?
Don't crush their dream. Instead, present to them the reality of what getting into music school will require of them. Show them standard audition pieces, etudes, and orchestral excerpts, and spend time in lessons going over how picky your student will have to be about performance quality in order to be a competitive auditioner.
Make sure your student knows what the audition scene is like. Especially in smaller towns like the one I grew up in, even the best musician in the school band program might not be good enough to compete at the college level. Encourage your student to audition for music festivals and camps so they can be around students from other schools and get a better sense of what their competition is capable of.
The Conservatory Boot Camp Workbook is another tool you can use to help your student see what a college music program would demand. It's written to help potential music majors who know they love to play music but aren't sure how to pursue further study in college. If your student can get through the 12-week regimen of Conservatory Boot Camp, they'll be much better prepared for the college audition process.
So don't write your student off, even if you're not sure they're cut out for music school. Some of the most talented, conservatory-bound people I know burned out in high school or early college and wound up abandoning music altogether. Natural ability only gets you so far before you have to start working to get good at your instrument. If your student wants it badly enough and is willing to put in the time and effort, they can make music school happen.