Every girl; to their underwear

"Well, you'll see." With that you walk in the middle of the room. "Hey, can all the girls please come over here?" Although some of them are hesistating every girl walks over to you. "So, I just wanted to inform you, that every girl in our PE class, except for Melody, has to wear only her underwear."

"Are you kidding?" A girl asks, but before you can answer her question all the girls, except for Melody, are taking of their shoes, socks and PE uniforms.

"Why are you allowing Melody to stay in her normal PE clothes?", another girl asks.

"I don't need to have a reason for any of my actions.", you answer, while your teacher gathers the class.