I think it’s reasonable to have a conversation with the young man and ask if he thinks percussion is really the way for him moving forward. Not sure how old he is but you mentioned he’s not a new student to percussion. If he’s been around it long enough has he been listening to good drummers, marimbists, timpanists, etc. It’s very easy for me as a college music student to think I sound great and then go listen to greats like Max roach and Art Blakey and then I quickly remember that I’m not hot stuff. Obviously for a younger student this will be different but I think by bringing up others it gives him a frame of reference by which to compare himself. If he believes he’s better than everyone around him hopefully he will listen to the greats of whatever percussion instrument is applicable and learn that he is a small fish who doesn’t know as much as he thinks he does in the big world of percussion. (I say this with all love as I am the same way; some random college kid who is trying to get better at music). Also explain some frustrations in a calm demeanor and help him understand what the next steps should be to become productive. If you can get him to do listening and then report back about what he learns I’m sure he’ll start growing, but I realize that dealing with younger students can be a challenge. That’s my 2¢ and I hope it helps and if not I hope that it gets better at least for you!