You pull out the list of lockers and combinations. "I actually don't think I'll change into one of these people. Do you want to change, though?"
"Yeah, why not? I want to try to be someone else today, for a little while, but not too long. I think you should, too, dude."
"Okay. But I'll let you go first, Brian, who do you want to be?" You hand the list over to Brian.
"I think that I'll change into Finn." Finn O'Conor is a really athletic kid, but nicer than most of the jocks at the school. More importantly, and unlike most of the other jocks, he often leaves a pair of shoes in his locker. "I think it'd be interesting before I change back into my old body—your current body. You know what? I'll just call it your body for now."
"I'll change into Finn, too. We'll see what happens. I'll let you change first, though."
"Deal, dude." You take off your shoes and socks and go to your backpack. You pull out the magic socks from the backpack and hand them to Brian. Brian takes off his own shoes and socks and puts on the magic socks. He walks over to Finn's locker and puts in the combination for the lock. He opens up Finn's locker and pulls out a pair of Finn's shoes, as expected. "Yuck. Finn's left some dirty clothes and underwear in here." Brian slides his feet into the shoes. Brian's feet stick far out the back—Finn, though older than Brian or Adam by a year and also an athlete, is a very small kid, at least for a thirteen-year-old.
Brian's feet visibly shrink to fit the shoes, and he shortens by three or four inches. His body grows really thin, and his pants fall down. Luckily, his boxers stay on, but they're clearly loose. His shirt is clearly just dangling on to his now-really-thin shoulders. He pulls up the shirt, and you can see his ribs. He has muscles, not well-defined, but more than most kids his age or size. Brian's eyes change colour from brown to bright green. His hair shortens to about one inch long and changes colour to a very bright red. His skin pales, but bright freckles come into existence across his face. He stops changing after about a minute.
"Wow," Finn says. He is Finn now, not Adam or Brian. His voice is about the same pitch as yours, but slightly different. It's also got a very slight accent. "Okay, your turn." He pulls up his pants, but they fall down again, so he pulls them up again then sits down. He hands the shoes and socks over to you.
You put on the shoes and socks, and you begin to feel slightly queasy, marking the start of the transformation. Your feet don't need to shrink much—they are already almost small enough to fit in Finn's shoes. You only grow shorter by an inch or two. Your clothes a lot feel more loose, but they don't fall off. You gain slightly more muscle, but you don't really lose any weight. Your skin stays almost the same pale shade, but your freckles become more obvious. Your eyes change from blue to green, and your hair shortens and becomes bright red. The queasy feeling dissipates. You are now Finn, and so is your friend.