Almost everyone is quiet, but then one boy raises his hand shyly. "You can do me," he mumbles, as if ashamed to admit he'd be OK with it.
"Thank you for being so brave," Ms. Wells smiles, and she comes up to the boy and taps him. He winces as the magic transfers to him, and you all watch transfixed as the opposite of the change that just happened to you starts to affect his body. "I know you'll make a beautiful girl," she purrs.
His short black hair quickly cascades down his back, almost seeming to soften as it lengthens. His skin softens and its thin covering of hair seems to vanish, while his face contorts and adjusts. His cheeks appear softer, his lips puffier, his jawline smoother.
He pants and groans, and the pitch of his voice heightens. "This... I like this feeling," he admits in his newly feminine tone. Tiny clicks ripple through his body as the magic starts to affect his muscle mass and figure. His arms and legs shrink in both length and size, and his shoulders shift closer together as his figure curves inward slightly. His clothes look way baggier on him now.
A keening moan escapes his lips as his nipples tent his T-shirt, and he mumbles, "I'm sorry, I have to take this off!", pulling it up and off his head, not even noticing how he pulled it from the bottom like girls tend to rather than the top like boys tend to.
"Don't worry about it!" Ms. Wells said comfortingly. "We don't judge anyone for their bodies in this room, nor how they change."
"Th-thanks," the now shirtless boy gasped as everyone- particularly you- watched in amazement as his chest transformed. The nipples swelled and expanded far beyond masculine proportions, and he breathed heavily, large mounds emerging on his chest. Before long he had sprouted D-cup breasts, and by looking at them you were reminded how your own body and sexuality had changed. You felt a desire to cup and play with them, and to suck on them.
At last his crotch and hips started to reshape to the whims of Ms. Wells' spell. In an attempt at modesty he pulled his T-shirt back on, but then blushed as he felt something clutch at his lower body and undid his jeans and removed his boxers with shaky hands.
The curve of his torso became accentuated by the curve of his hips as they widened out to make up for the narrowing of his shoulders, and his butt enlarged behind him, appearing soft, smooth and thick, making you think how you'd love to cup or slap it.
Only the most masculine part of his old form was left, and all of you had a great view of his penis as it slowly shrank away. His balls tucked up into him, and with two wet pops were pulled from his scrotum, which receded to a small mound before the seal down its middle peeled open to form a vaginal slit.
As his penis became smaller and smaller, you felt yourself developing an erection that was rapidly becoming larger and larger. Seeing this boy be emasculated was the most arousing thing imaginable to your new body, its maleness desperate to fulfill its primal desire- and knowing the boy who would soon be a girl was a perfect fit.
Once his penis had shrunken to a clitoral nub and settled into place above her new vagina- since you felt like your pronouns had shifted from feminine to masculine with the transformation, you figured hers would've too- she crossed her legs and blushed as she felt your eyes on her. She could smell your masculine musk and you could smell the scent of her female juices moistening her up as she glanced at your phallus. You two couldn't think of anything but indulging your masculinized and feminized fantasies now.
Just as your interests you considered gendered have shifted, so has your sexual desire. You ached to play with her soft body, hold her down, fill her with your cock and mate her. That fantasy felt almost impossible to ignore, and even moreso by the second...