At your sons age Showcases are nothing to lose propositions. I would tell him that.
Most schools are not going to ask kids to commit at that age anyway. My son did some reach school showcases at that age and did not impress. He came back a year later with added strength and opened some doors.
There is nothing to loose(except some of your $$) and everything to gain. In my sons case he learned how to showcase at his first two at age 15. After that he was never nervous. If he has a bad weekend than it is a good learning experience. If he has a good weekend that is a bonus is the way we approched it. It is also an opportunity to begin to see what level your kid can compete.
Good Luck and Tell him to have fun. He is playing ball afteralll and its better than picking weeds no matter what happens!!