It was the smell that hit Ty first as he looked up. He could smell horses, but not just horses. Mares in heat. His new equine member swelled in response. Everyone was hung like a horse, so the girls now sported the genitals of mares. Instinct seemed to have come along with the endowment, and the males in the class began to rise and bump each other for dominance.
It was only as Ty was jostling with Jason to get closer to Cindy, that Ty noticed Jason's pants were being pushed down by what looked like a hairy brush sticking out of the back of his boxers. Jason flicked it as Ty nudged him. Ty looked down at his hand, it was cramping up. He realized it was changing into a hoof. He looked at his hands, but the smell from Cindy was stronger. He shouldered Jason. He welcomed the transformation because his bulk was growing too, and he moved closer to Cindy. As their bodies swelled to equine proportions Ty, Jason, Cindy, Mr. Bretman, and their classmates ripped their too tight clothing from their bodies.
Fine coarse hairs sprouted all over. Soon the room was crowded with naked horny stallions and mares.