"You can't teach sound." Wise words from a fifteen-year-old. How can anyone convince an intelligent child that a piece of music is the same on one piano as on another? It isn't. Nothing about it is "the same" except perhaps a theoretical scheme that abstracts from the sound a kind of logical procedure with identifiable elements.

But that isn't the music.

No instrument begs the question as much as the piano, for there is no such thing as "the" piano. Maybe that's why piano instruction is so regimented as to deny the very nature of each instrument we play and why musicians who play sonatas "For Piano and ..." fail to listen to the particular piano with which they play.