Give her the key to lock the door.
From Create Your Own Story
You stroke her thigh with one hand and with the other reach into your desk and pull out the key to the classroom door.
You hold it out to her and casually say, "You wanna lock the door? Give us a little more privacy?"
She grins, snatches the key off you, and runs for the door. She's almost skipping.
You hear the click of the lock and she spins around to lean on the door, savouring the moment. She gives you a wide, excited smile, seems to think for a moment, then adopts a wry confident expression. She stands up straight and begins a slow, sultry walk towards you, one leg in front of the other, hips swinging. She raises her arms to fan out her hair then runs her hands down her body. It's damn sexy.
You smile and turn your chair to face her and her eyes widen as she sees the huge bulge in your pants.
"Oh my," she purrs playfully, "what have you been hiding in there all this time?"