You cum on her face, right after the bell sounds.

Tears stream down Sarah's face as you ruthlessly facefuck her, using her throat as your own personal fuck toy right in the middle of the locker room. You feel yourself getting very close, and as soon as you hear the bell go off, you pull out and point the tip of your cock right at Sarah's startled face, covering her in your cum. When you're finished, she moves as if to get up, and you have to remind her that the extra credit isn't over until you say it is.

She sinks back to her knees, head still tilted up as her makeup, her tears, and your cum drip down her face onto her tits. Once you're satisfied that she's obedient again, you wipe your dick off on the parts of her face not drenched in cum, and then begin to dry your dick off with her hair.

"Sorry, Sarah, but I can't pass you for that. The best I could have done is give you a 50, for effort, but then you tried to stand up before I was finished with you. Overall, you get a 40 for this period. You just aren't good enough."

You dress leisurely, Sarah trailing behind you, dazed from her first-ever facefucking, as she slips back into her slutty school uniform, having momentarily forgotten that her face is still plastered with cum.

Life is good.