There was a boy who was excellent at playing the piano i think

Theres one scene i cant forget, he was a little boy (if my memory is shit it mightve been a girl)

He went into his teachers classroom/office/music room or something and she was playing the piano, when he came in she stopped

She asked him to play the piano to show her how much he knows, so he sits down and plays exactly what she played and stops when she stopped because that was how far she got and he doesnt know anymore (meaning he remembered and could play exactly what she played a few moments earlier)