Encourage her, but subtly

You look down towards the hand rubbing your thigh, but along the way your eyes get sidetracked in the deep cleavage barely held into her tight, white shirt. With all the blood leaving your head, you have enough presence to remember that a real principal would worry about getting in trouble and proceed carefully. "Michelle, perhaps you could thank me somehow. Perhaps we could-"

Michelle leaps forward and kisses you. When she pulls back you see that she's standing over you and holding your cock. Somehow your pants have completely opened up and you've slid down in your chair until you're almost lying down.

The gorgeous girl leaning over you smiles super wide. She jerks your cock slowly for a moment, then leans over and sucks it deep into her mouth. This makes your legs rigid, straightening them out in front of you. She kneels down, pinning your outstretched legs between her strong thighs.

Michele sucks hard, then releases your cock with a loud pop. She leans forward and points your cock straight down, so the head is nuzzling between her breasts. She pushes it tight against her chest and moves forward, pushing your cock down between her tits as she moves closer to you. You lose sight of your cock and her breasts and she slides her body up yours, though you can still feel her large breasts pulled tightly against your cock by her bra.

She stops moving forward when your cock is buried in her breast like a key she hid in her bra. Her face is inches from yours, almost close enough to kiss. She moves back, then forward again, pushing her breasts against the top of your cock,.

After a few thrusts Michelle pulls out and slips your rod back into her mouth, all while gazing at you with those gorgeous green eyes. She runs her fingers lightly across your balls and you spasm. You're not going to be able to contain yourself much longer.