The next day, Rumble was in class, a little sweaty from today's "workout", namely flying to school because he'd overslept slightly. A strawberry flavoured toaster strudel still clutched in one hand, he zoomed there and landed safely, getting in just before the bell rang.

One thing that'd changed as the classes -and the school, (slightly) and the students...- grew was that the classes were split somewhat. One class was mostly colts, the other, mostly fillies; in their 'teens, the lot of them.

Cheerilee, the usual teacher, had aged pretty well, all told. She was in her fourties at least, but didn't look a day over thirty(1). She was typically smokin' hot, even for mares half -or so- of her age, but today she seemed particularly so. She was wearing a shirt and shorts combo that was about a quarter-size too small, causing it to hug her curves perfectly, leaving juuuust enough to the imagination.

Rumble wiped some sweat off his brow. He felt far hotter than usual, but dismissed it as just the summer weather.

Little did he know how wrong he was.

As Cheerilee etched equations on the blackboard at the front of class, Rumble did his best to concentrate, but was finding it especially difficult today, Cheerilee showing off, advertent or not, wasn't helping.

He reflexively reached down toward his crotch, only to recoil as a jolt of pleasure thrummed through him, causing his eyes to widen. That was awfully good for just a touch.

He had to do that again.

Slowly but surely, he stroked his aching member, waves of pleasure undulating through him. He went one more time to finish the ride...

Only to find nothing there.

Reaching further along, he found that his cock was far shorter than just a moment ago. It felt just as good to the next touch, and was just as hard, but just after that, it shrank by an inch, then another. Before he knew it, his old friend was gone, no trace of it left. A spike of pleasure ran up his spine as he felt a strange sensation from the other side. He could easily guess what this implied.

'Okay.' he thought to himself, -rather, herself- 'That potion thing was a bad idea.'

His -rather, HER- body was adjusting bit by bit, shifting him -her- piece by piece into the ideal form of an adolescent mare. Her hips were widening, her breasts expanding, both packing on subtly supple layers of fat. Rumble's coat was becoming softer and her previously chiseled male face began shifting into a mare's softer, more curved muzzle.

Just then, she also noticed the male musk permeating the room. The fillies in this class had better control of themselves than she'd used to think. The fact that they weren't constantly thinking about the males on the other side of the room was a testament to their integrity. Rumble, however wasn't so lucky.

Her new marehood was leaking, making her nearly lose it every time she winked. This pretty much conclusively marked her as playing for the other team, if it wasn't clear already.

Her breasts expanded by another half inch, reaching a C cup by now. As her expanding breasts began to press against the shirt that he had picked out, demanding room to grow, she felt something else that was strange. As her breasts pressed further... she felt fluid begin to slowly leak from them.

Rumble's eyes widened. Was she actually producing milk? Why? Even changing sexes entirely shouldn't have caused that!

Suddenly, Cheerilee paused and double-sniffed the air. Few knew how sensitive her senses were. She was even able to adjust her sense of smell and hearing to detect even the most subtle of odours or sounds.

And right now, she smelled a mare in need, at the back of the class.

"Rumble?" she queried, raising one eyebrow.

Rumble tried to lower her voice to its normal tone. "Yes m-"

"Rumble? Stand, please." the teacher demanded.

Face flushing, Rumble did as she was told, revealing her new form for everypony to see.

There were some gasps, some stunned expressions, a couple of snickers (particularly from Diamond Tiara and Silver Spoon, who were fortunately separate from the Crusaders, who were in the other room) but the most common reaction was wolf-whistling.

Cheerilee said, "Let me guess. Heat season?"

"Yeah."

"Felt inadequate?"

"Yes."

"Needed a solution?"

"Yes."

"Apple Bloom, I take it?"

"Correct, ma'am."

"Potions?"

"Yes."

"Dropped 'em?"

"Uh..."

"And the two of you took the wrong ones because neither of you thought to colour -or even label- your potions differently?"

"... That's about the size of it, ma'am. I think it's still in effect, too. We were going to take them immediately; It didn't seem important."

Cheerilee facepalmed and sighed. 'Of course. they never think of that.' It was going to be one of those days.

"Well, this could have happened to anypony, had they done much the same. Well, it's time for the Sex Ed portion of class anyway. Might as well make the best of this. We should still have about..." Cheerilee checked the clock on the wall. "Twenty minutes? Plenty of time."

She looked back at her class. "Alright. Some of you will know that Heat Season is coming soon. It's very possible that Rumble here will spend that time as one of the mares; Talk about learning how the other half lives." she joked at the end, also getting scattered chuckles from some of her students. "Here is how we can relieve a mare in need of it - without actually risking becoming a parent, if you take my meaning."

"Now, those of you who have read The Guide(2) -as you've been instructed- will know much of this, but..." she made a come-hither gesture to Rumble, indicating that she also turn around; Then she went around to stand behind her. "Rumble, -for ease of use, Rumbelle(3)- being a Pegasus will have different sensitive spots from, say, a typical Unicorn mare. In the guide these are called... -What, Pipsqueak?-"

"Petty-Zones, ma'am." Pipsqueak answered smartly.

"Very good. You get a star." Cheerilee said, nodding. "For example, we can tell what level of need she's in if we touch Zone One. This, on a Pegasus is... -Where, Button?-"

"Uh... her back, I think? Starting between the wings.(4)"

"Very good. A star for you as well. Now, if you stroke a Pegasus mare like sooo..."

Cheerilee drew a finger down Rumbelle's back. Not even a fifth of the way down, she began turning pink and her knees buckled. Her wings also extended fully.

"Ooh, Rumbelle here is DEFINITELY in need of relief. Surely many of you will have noticed Rumble's colour change. This is not a blush, but called... -Twist?-"

"Pet-me-Pl'th, Mith Cheerilee." Twist slurred. "It'th much eathier to thee in lightly coloured mareth, ma'am."

"Excellent! At this rate, I'll need more stars. It should also be noted, though that white mares have a cuddle factor of 650 -what, Featherweight?"

"M-Micro-Lunas, miss Cheerilee." Featherweight said, a little nervously. "Titled after Princess Luna herself."

"Good, good. Now, activating the pleasure centers -the Petty Zones; this process is also called 'tapping'(5)- will elicit a much stronger response. Now, if we tap Petty Zone twoooo-" Cheerille touched the base of Rumble's wings, eliciting a throaty moan; "Threeee..." She stroked around her subject's neck, causing her to nearly black out from the jolt of pleasure that ran through her; "And four..." she continued, touching Rumbelle's sides, just below the ribcage, causing her to instinctively roll over and lie still, breathing heavily; "You'll have full access to the rest." she elaborated as Rumbelle 'pinked' much further. Cheerilee got down on her knees, to Rumbelle's left side.

"Now, over here, we have Zone Five." she said, indicating Rumbelle's underarms, about in line with her heart, "Which is on both sides." she continued to explain, stroking both sides at once, causing Rumbelle to stiffen from the shock that ran up and down her spine.

She was largely unaware of what Cheerilee was doing, only that she was in heaven, feeling jolt after jolt of pleasure. Her breasts and ass were still slowly expanding, her hair growing longer still.

A button on her shirt popped off.

"Zone Six will be along the upper arms..." Cheerilee continued, stroking the indicated spot, causing Rumbelle to begin breathing even harder.

Cheerilee also noticed one of the other side effects of the potion. "Oh! It seems that Rumbelle is also lactating. I'm sure you can guess what Zone Seven will be. Diamond?"

"Uh..." Diamond Tiara started. Had she read the book? As distracted as she was by the current lesson, she couldn't for the life of her remember! Her mind was a total blank!

She stiffened. Was she actually getting turned on?! "Uhhh......"

Cheerilee rolled her eyes. "Silver Spoon?"

Silver answered, "Her nipples and the area around 'em, miss Cheerilee. It'd also be a good idea to have a container prepared."

"Excellent suggestion, Silver Spoon. Two stars for you." Cheerilee said, putting her words to action. Coming back to Rumbelle's prone form with a plastic jug, she pressed the needy young mare's left breast lightly, causing a small dribble of milk to emit. Pressing harder caused the miniature stream to widen, flowing into the plastic bottle at hand. Upon releasing, she saw that Rumbelle's breast had shrunken slightly... but not by much. And the jug was already a third full.

Snagging another jug, just in case, she continued her ministrations. "Now, if Apple Bloom had drank this potion, as they had planned, this likely wouldn't need to happen. As things stand, I'm sure she's in a position to be 'milked' herself, by now."

Stream after stream of white fluid flowed into the containers, swiftly filling them. By this time, Rumbelle's breasts had expanded to a DD cup, and two more buttons had popped off, revealing more of the white cantaloupes previously stuffed into her shirt.

Cheerilee noticed that the shirt Rumbelle was wearing was swiftly approaching 'nearly useless' status by this point, and was merely in the way. Acting quickly, she pulled on what remained, causing the final few buttons to snap off.

After this, the full size of Rumbelle's newly grown breasts was revealed; swollen to an E at least, if not more. And by this point no more milk was comming out. 'Just as well.' Cheerilee thought, 'These were nearly full anyway.' she said to herself, capping the bottles and putting them aside.

Seeing that time was nearly up, Cheerilee said, "Since we're almost out of time, I'll direct you to Zone Ten." So saying, she pressed just above Rumbelle's belly button, causing her to faint entirely, with a final loud sigh of pleasure.

"And that, students, is what you need to know for today." Cheerilee said as the bell sounded a few seconds later.

"Now," she wondered aloud, "How is Apple Bloom dealing with this situation?"

Author's Note

1: Yes, I'm aware of how equines age, but Ponies have rather long lifespans, in canon. So for the purposes of this story, they mature much like humans, but still live FAR longer.
2: Reference to

TThe Definitive Guide to Pony Anatomy - Starring Princess Celestia and Princess Luna

• MLP: FiM
• Comedy
• Slice of Life

Should you find yourself a visitor to Equestria, it would benefit you to be able to tell a pony's rubby-tubby from her boop-button and fuzzy-wuzzy. Herein is your definitive guide. (Clean family-friendly comedy, absolutely nothing explicit)

• Human
• Celestia
• Luna
• Other

Pen Mightier · 2.7k words  ·  1,746  30 · 27k views

3: For the purpose of this 'lesson', I'm running with this nickname.
4: Yes, I'm aware that zone One is supposed to be the ears, but as a Pegasus, she's a bit different.
5: As in tapping a resource.