I'm a music teacher in public schools and this is what I observed as well. Almost every single kid signs up in the beginning, but by 6th grade, kids that just can't cut it tend to drop out. Those same kids are often struggling in their other classes as well. Very rarely do you have a kid who excels only at music and is flunking their other classes. I have two students like that right now, but they aren't slow, they have terrible home lives that screw with their school life.

Howard Gardners theory of multiple intelligences just doesn't seem to apply in any meaningful way - I've never taught a kid that was gifted musically that wasn't also smart in most other areas. By smart, I don't mean only scores well on a test, I also mean kids that have a sharp sense of humor, think critically, or can reason through something without being led by the nose