Gladion--or "Asher" as people in the school generally know him--isn't in the music class in question. He's just in the hall in between classes while the teacher writes on the board, and he wouldn't have given the room a second glance if he hadn't seen something really weird while he was passing by.

He pauses at the doorway and turns for a closer look, and there is absolutely a swan standing in front of the board. A really big swan who seems to be writing a music lesson. But then he blinks and suddenly it's... just a teacher. But he was sure...