Several hands went up, and Cecily picked a good-looking blonde boy, who came up after a moment's hesitation. "Thank you," she said kindly to him. "So, what's your name?"
"Lucas," the boy replied.
"Nice to meet you, Lucas," said Cecily. "So if you're OK with it, you'll be the subject of our first lesson." The chalk started to write again, and Lucas turned to read it- "Sex transformation"- blushing as he processed the words. "By the way, just to be clear you can back out at any time if you aren't comfortable with being transformed!" she told him softly. But Lucas shook his head and stayed put.
"Sex transformations are the type of transformation I start with because they involve the least complex changes," Cecily explained, turning to the class. "The only thing that needs to be transformed about your genetic makeup is one chromosome of the sperm that your body formed from, and boom, your whole body changes sex." The chalk drew a sperm with a Y chromosome and one with an X chromosome to illustrate her point. "It's a simple, and fairly safe, spell to learn. And also pretty eye-opening," she laughed. "Sometimes being 'Cecil', as I like to call him, is quite fun."
She turned back to Lucas and asked him, "So are you ready for me to transform your sex?"
"Ready as I'll ever be," Lucas replied.
"Would you be OK with undressing so we can watch the changes? Like I said, there's no shame here."
"I guess so," Lucas answered, blushing and shyly starting to undress. Cecily sneaked a few peaks at the handsome young man, and once he got naked she noticed he had an erection. Clearly all the talk of changing sex was turning him on.
"Great, so now we have a perfectly normal male human. And this," Cecily pointed to the chalk drawing something, "is the sperm cell which provided his Y chromosome. Now, all you have to do to change the chromosome's type is to focus on it and project your will to invert it. Learning to project your will is a key part of transformation, so if you want to try it on your own chromosome, you can do. Watch how Lucas's chromosome changes when I will it to..." Sure enough, as Cecily focused the proportions of the chromosome in Lucas's sperm started to change, and it had turned from a Y to an X.
Lucas felt a weird unfamiliar warmth surge through him in response. "Since we've changed that, Lucas has switched from genetically male to genetically female, and his body will start to reshape in a sort of chain reaction." That phrase felt very apt to the boy- who of course was now becoming a girl- and he heard Cecily describe transformation after transformation as he saw his body change and felt strange pleasure course through him. "It looks like his figure has already started feminizing, he's slimmed and his figure has turned more curvy... his muscles have turned less pronounced and more lithe, and his hands and feet are smaller too... there go his wide masculine shoulders... his facial features are turning more girlish now, and his larynx and neck have shrunk... see how his nipples have swelled because of mammary glands forming in his chest?... and he's starting to sprout breasts, which are forming the centre of a second erogenous zone... his penis has started to shrink away now, and it's lost the capacity to ejaculate... his balls have moved up into him now and his scrotum is turning into a vaginal mound... his penis has almost finished its shrinkage, and is forming into her clitoris... and, there we go! A vagina has formed between her legs! Lucas- or I guess Lucy would be more accurate now- is fully female!"
Lucy felt stunned as her body's changes finished. She really was female! She looked it, she felt it. In fact, looking round she noticed a bunch of people who had either been the opposite sex before or were still transforming into it. She turned to Cecily in amazement, and the teacher assured her, "You look really pretty, Lucy."