It can be a challenge to teach a student with a good ear. You need to be careful about playing music for kids with really good ears. If you play the song before they’ve tried to read it, they’ll often skip reading the notes and just play the music in their heads.
For example, my wife has an extremely good ear. She told me a story about taking piano lessons as a girl. She’d listen as the teacher played the song. Then, she’d play it back from memory. Once, when she played a song, her teacher said, “Uh… good, but you played it in the wrong key.”
That explains why Charles Rosen suggests that teachers should avoid playing for students with good ears. Because they’ll give the impression that they can read music when they really can’t.
It’s also my experience that if you play for them, they’ll avoid reading, because they find it easier to play from memory. I had one little boy with killer ears who once asked, “Can you play me the song?” I told him, “No, if I do that you’ll play by ear and skip reading the music.” Then, he got a darn-he’s-on-to-me expression on his face.
This shows why it’s so hard for someone with a good ear to learn sheet music. Because some students want to take the easy way out. However, many students legitimately struggle to learn to read.