Some might call it math...

"Now today we are going to get into the subject of what defines the grad of increase of a function. This is called f'(x). Would anyone like to help me present an example?" Once again no one raised their hand. Mr. James's classes usually were not really well liked, so nobody participated willingly.

"Diana. Please come to the front so we can give an example together." You knew Diana. Everyone did. She was "boobie girl". Or at least that was what she was called behind her back. Her tits were not even that big. They were actually rather small when compared to some other girls who were in your school. A happy D cup. The reason why she had been given such a nickname was that she had somehow managed to convince not only her parents, but also a surgeon to give her implants... when she was only 14 years old. You don't know the whole story, but well, the name stuck.

At this new kind of school Diana was probably well liked with her breasts. Her Jacket was off, not a big deal, since most of the girls were not wearing theirs. She still wore the rest of the uniform. A tie, the blouse, half way closed, her bra and even the skirt was rather long. Her hair was a dirty blonde and short cut. She was a nice girl, but beside her breasts, there was really nothing to select her over any other average girl.

"Diana, please do us the favour and turn towards the class." He was being so polite to her. Whatever was happening, it must be something he really had been waiting for. "Get on your knees please, it will be easier to demonstrate it then." She was ****, but obeyed his command. Her breasts were being pushed out in this pose. Every guy in the class either thought about her lips or her breasts at this second, you were sure about that.

Mr. James turned to his desk, opened a drawer, and took out a purple dildo. It was not a really wide one, you would have guessed about an inch, maybe 1 and a half. But it was long, possibly 15 inches. Maybe even more.

"I asume you are all familiar with the metric system, because in this example, we will use cm. Just for those uneducated, 1 inch is 2,54cm" He walked behind Diana, who was already shaking in anticipation of what was going to happen.

Softly, almost caringly, Mr. James put his hand around her face, going down towards her neck and then just pulled her face up, so she looked straight up into his eyes.

"Open your mouth." She whimpered at this command.

"Do I have to participate in this example? I would rather just watch." She asked, but the response from Mr. James was just a sadistic laugh as he did not even remotely attempt to hide his amusement.

"You can go back to your place and sit down if you want. I will select another girl. Of course I will have to mark you down for refusing to participate in class. You would receive an "F" for today." She froze in shock for a second, then instantly opened her mouth wide. As far as she could.
"Good decision."

He placed the dildo's head on her lips and started to explain.

"Now, the start function we are going to discuss is f(x) = 2X. So in step 0, I will put it 0 cm into her mouth. Now in the next step" and he slowly went down with the dildo, entering her mouth, "we insert it 2 cm deep into her mouth. On the second step, we go 4cm deep" and so he did. Not even focussing on the class remotely, he just looked at Diana.

"Now, for example, who could tell me, what we would have to do, if X would equal 5, 7 or 9?" There was a slight pause when, to your big surprise, Tommy raised his hand.

"Yes, Mister Lyn?" The teacher asked without looking up. "You would have to put it 10, 14 or 18cm deep into her mouth."

"Exactly. 10! .... 14! .... or 18 cm deep" while saying the numbers he pushed the dildo in about that deep. Diana was already gagging on it as he pushed it 14cm in and as he went way over that with the full 18 cm, she tried to cough it out. Without a chance. Mercilessly, he held it in her throat, forcing her to hold her breath.

"So maybe you can answer another question Mister Lyn. At which amount are the cm's increasing, if we increase X by one." He kept it in her mouth while talking. It must have been 10 seconds already. 15... 20... You looked to your right to see Tommy staring at her mouth and you hit him on the arm. "Answer, dude" you whisper.

"Oh, ehh... 2, I guess." As he said that, Mr. James released poor Diana and pulled the dildo out of her throat. It was covered in her spit and her eyes were already filled with tears, running down her face. He was still holding her face in the position with the face up, so she couldn't put it away, but she tried to cough in order to clear her throat. Although we was able to spit, it landed mostly on her face again. Snot was running down the sides of her nose, making her look messed up to a degree that was almost gross. Even worse for you, your manhood seemed to be starting to awaken.

Why now? Why not when I saw the girl undress. Why not when I saw the girl sit on her buttplug, why not even when I saw the girl in the slutty heels or with the ball-gag? No, I am getting hard from seeing her spit on herself? Why, dude you asked yourself/your penis.

"Now, quiet please everyone. We have just discovered, that the differentiation of the function f(x) = 2X is 2. This is written, as I said as f'(x) = 2." He wrote it at the board. Diana used this time to bend forward and spit on the floor as much as she could, as well as to lift her blouse to clean her face.
The fact that her makeup was now even more ruined, and also her blouse was now no longer white did not seem to bother her.

"So what if it is a more complex function than 2X. Let us for example go with the classical square function. f(x) = x² . Let us try this next." To Diana's very evident shock, Mr. James grabbed Diana's chin again, lifting her face up as she had been before, thrusting the tip of the dildo just between her teeth.

"x = 1, so x² equals what?" He asked the class, and a murmured "One" was the answer.

"Good, so what if x equals 2?" again the answer was not very enthusiastic. You do, however realize that two girls had answered the question and they were doing so with a bit of panic in their voices. They were most likely thinking that if the answer was given, Mr. James would remove the dildo from Diana's throat, like he had when Tommy answered.

"Right, 4cm in" and he sunk the dildo in deeper. So now x equals 3" This time the rest of the class did not have an opportunity to answer as the two friends of Diana immediately called "Nine!"

"Correct. Nine centimeters deep in her mouth it goes" And he did begin to slowly lower the dildo further, bit by bit sinking it into Diana's waiting mouth. "So, Kimberly, maybe you know the next answer as well. So what would we get if x equals four?" Of course she did know the answer. But remembering how Diana reacted the last time as she was penetrated in her mouth this deep, she hesitated. "No? You don't know the answer?" Slowly she shook her head.

"To bad, from this point on, I want you to stop calling the answers. I will call your names if I want you to speak, so raise your hands if you know the answer to this one." No one raised their hand, not even Tommy this time, even though you see his arm move a bit.

"To bad. It is 16 centimeter deep" And so he pushed it in. Diana's scream was silenced as it slid into her throat, once again. You were amazed that somehow she was still able to breathe. Her breathing, which actually sounded more like a gurgle, was so heavy and loud that everyone could hear it.

"Now can anybody tell me what you think the differentiated function is here? How many centimeters deeper do I have to go every time I increase x by one" He keeps the dildo in Diana's mouth. Her salvia is leaking out again already.

Kimberly took up her hand and while Mr. James clearly saw it, he ignored her completely.

"Nobody? Maybe you will get an idea if we go a little further in the example." He looked at the class. Kimberly's hand was wide up, already almost waving at him. You hear her whisper. "Please... please just ask me. I know it."

"How many centimeters more will I have to put in her mouth, if we increase x by one now. Yes? Kimberly. You know the answer to that?" He asked her, before she could take down her hand for this question.

"No, sir, I know the answer to the previous one, the diffe..."

"It is to late for that. Do you know the answer to my current question, or do I have to put you down for detention for bringing up something that is not related to my questions?" Her face turned white. You did not even want to know how bad detention would be.

"Its.... 25 cm, so you have to go in 9 more..." She whispered. Diana screamed even before it happened.

"Exactly, so let me demonstrate this. Diana is currently happily sucking on 16 centimeters of dildo. We will shove 9 more into her throat now." He forcefully lowered it further. You could see her throat being filled by it, having it full on display, with her in the neck. "So we have reached 25 centimeters. Before that we had put 7 centimeters more into it, to reach the 16 from our basis of 9. Can anybody guess now, what it could be. Mister Lyn again, maybe?" He looked over at Tommy.

Considering that Tommy always sucked at math, it was not a surprise that he just shook his head.
Diana was also shaking already, but not only her head. Her whole body was trembling and her face was about to turn blue.

"Well I will tell you then. f'(x) is 2x. The amount you increase is also in relation to the variable x and not a constant as in the example prior to this one. Did everyone get this?" He still had not removed the dildo from her throat, let alone mouth.

Diana was truly gasping at this point and trying to escape as the sex toy was taking her breath away quite literally. She soon fell forward and only after she hit the floor did Mr. James pull the dildo out of her mouth. Diana had landed right in the fluid she had spit up on the ground after the first example.

Her mouth still open, even more salvia drooled out, mixing with the snot out of her nose and the tears which were streaming out of her eyes.

"Let her be!" Mr. James barked at Kimberly, as she was about to stand up to help Diana. "All of you, please read chapter 4 of your study books. The first page should give you an overview of what I had just showed you for better understanding."

Apparently this scenario was not all that unusual, since everyone picked up their books and started to read. You decided that the incident could not really be all that bad, because even "future you" would not have let someone die right before your eyes. Also, if something happened today that you REALLY disagreed with, you could just change it later when you are "future you". At some point you must have already accepted all of this as being good. So why not just try and accept things as they happened. With that thought, you took out your book and started to read.