Pedo Romp/Have her get naked for the spanking
"Nekkid?"
You nod. "That's part of the deal. Do that, and I won't hit so hard."
With less shyness than you would expect, little Cindy takes off her shoes, then gets up and starts pulling off the rest of her clothes. No bra at this age. You can barely breathe as she lowers the Seventh Veil and her whole magical little body is revealed to you. You keep the smile off your face, though - your serious look is part of the plan for control.
You pull Cindy in closer to you guiding her into place between your legs and then leaning her over your one knee. She goes quietly as this is the way her parents also spank her, bent over their knees. (You doubt, however, that her father has a hardon like this or a tiny stain of precum on his pants.) Resting a hand on her back to keep her in place you try and settle her nerves, "Don't worry, Cindy, I won't be too hard on you." And at that your hand comes down on her bottom with a "smak!"
Remembering the terms of the deal, she muffles any cry. Keeping the blows light, you strike her bare butt three more times. Her naked little body wriggles on your knee, and the sight and the feel are so exciting, if you keep this up, you think you'll do something you've never done before: achieve orgasm in your pants without actually touching yourself. Probably not a good move - you didn't bring spare underwear to school. So how to proceed?