Make her suck you off.

"Well, Sarah, since it was supposed to be a sexual exam, I figure we should keep that theme going. If you can make me cum with your mouth or throat before the next class starts, I'll give you a passing grade. The better you do, the higher the grade will be. You won't be allowed to touch me with your hands, as that would be cheating, but you can of course touch yourself."

Sarah blushes, and looks at the clock. Ten minutes. "I'm very new to this; nobody's written my name down since the rule started, so I don't have any practice. Still, I'll do my best."

She gets down on her knees, and looks up at you like she expects you to pull your dick out for her. You shake your head 'no', and tap your wrist to remind her of the time limit. "Oh, shoot, already losing time," she says, as she begins to use her teeth to pull down your gym shorts. After a few seconds, she manages to free your already-hard cock, and as it snaps to attention it drags a line of precum across her face.

Sarah gasps. "Oh! Didn't expect that..." her voice tapers off as she starts to fit her mouth around the head of your dick. You pat her on the head, "Always look up at me when you suck my dick, Sarah,"

She nods slightly, and then looks straight up into your eyes as she massages the tip and shaft of your cock with her mouth and tongue. You check the time, and say, "You're a minute in, and not quite halfway down the shaft. I do expect you to use your throat for this, you know."

Sarah looks a little pissed at you for the way you reminded her, but she starts to **** herself down further on your cock nonetheless. You intended to let her proceed at her own pace from there, but after a couple of minutes of watching her try and push her lips to the base of your dick, you took pity on her.

"Look, you're definitely not going to finish in time like this. How about you put your hands to work on your pussy and ass, and I just facefuck you until I cum? If you stay conscious until I'm finished and I get off before the bell, I'll still pass you. Start fingering your holes if you're going to do this extra credit."

"Ugh, that lucky bitch..." You hear Julie say from a few lockers down. You'll have to remember that; clearly, Julie wants some extra credit, too.

Sarah looks a little confused, but excited that you've given her an easier goal. By now, sucking your dick has gotten her pussy extremely wet, and her ass is still lubed up from the exam, so she starts fingering both of them - she uses her left hand on her pussy, and her right hand on her ass.

True to your word, you grab her head with both hands, and **** her head down on your cock. You feel a little resistance from her throat, but you change your angle a little bit and manage to push in a bit further. Finally, your dick slides into her throat, and you feel her lips press up against the base of your shaft as she starts to violently gag. You hold her there for a while, and the gags slow down, but she's crying now, and her mascara is running down her cheeks. You almost feel bad, until you realize that she's crying from the gag reflex, not because she wants you to stop.

You keep holding her head down on your cock with both hands, watching her eyes glaze over as she starts to lose consciousness. Before she passes out, you pull out just enough to let her gasp in some fresh air through her nose. After two breaths, you thrust back into her throat, and you can feel her body shake as she starts gagging again. You continue this cycle for a few minutes, until the feeling of her throat tightening around your dick finally causes you to tense up. You rapidly fuck in and out of her throat as you approach orgasm, and you can see that Sarah has three fingers each stuffed in her pussy and ass.