"Just change me back!" Juan said through gritted teeth. Mr. Mendes shrugged and pulled out the book he'd brought with him. He muttered a few words under his breath, and put it down.
"Now, class, as you can see, little Juan here is an ordinary first-grader, but he's going to show us about puberty and we'll see some of the changes first hand. Let's just take a look, shall we?"
As he spoke, Juan began to grow, his shirt and pants becoming tigher. He became uncomfortable as his height grew, buttons popping off his shirt, exposing his chest, which was losing the last of its baby fat. The sleeves began to tear as well, and then across his broadening shoulders, and soon the tatters of Juan's shirt fell to the floor, leaving him naked to the waist as he approached 10 years old. His pants ripped at the sides, more and more of his brown thighs being revealed. Juan blushed as his zipper unzipped itself. He wasn't wearing underwear, and the class oohed when Juan's penis, already sporting a bit of black hair around it, pushed into view from behind the ripping material.
"Now, Juan, don't cover it," Mr. Mendes admonished as the now-12-year-old Mexican boy reached down. "Raise your arms so we can see what's happening underneath."
Juan reluctantly did so, and the class got a view of the first few hairs sprouting under his arms. Like his pubic hair, it was rapidly filling in and spreading. His penis grew longer and thicker, and changed in color to a darker brown than the rest of him.
As Juan approached his original age of 14, hair sprouted just below his navel, and dark peach fuzz appeared on his upper lip and chin.
The class was silent in shock of what they'd just seen.