Better grades are for the dirty, 'A' is for...?

"Yeah... You really are a dirty little girl, aren't you Ms.Stein?" You grunt down at Nancy as you slowly fill her up with your cock, at the same time burying your thumb as deep as you can in her tight ass while you listen to her soft groaning.

"Uh-huh...!" She moans with only slight discomfort in her overly sugar-sweet voice as she smiles back at you over her shoulder, her blue eyes winking just as invitingly but at the same time keeping a wary watch over what your hands are up to. She seem to relax a little as you start humping her though, obviously dirty enough to enjoy a nice fuck and especially so if it can better her grades, allthough it's just as clear that she's still not quite as fond of where you've placed your thumb.

After a while of simply fucking the young student and letting her get used to your size and your finger up her butt, you eventually pull your hands back and grab at her firm hips. This obviously unnerves her a little at first as you can feel her tense up while you try to change her position, but she's still quite quick to follow your directions and bend forward so that she end up lying on her chest and face upon your desk while swaying her back to leave her buttocks high in the air.

While this new position allows you even deeper penetration of her welcoming pussy, she must also realize it makes her backdoor a more **** target since she's immediately getting more worried again as you make only a few more thrusts before pulling your dick back out of her. Her eyes follow your moments closely as you knead her firm buttocks, and seem quite surprised as you get down out of sight behind her and start working your tongue on her dripping crotch.

"Oh...?! That's... Mmmm....!" You hear her mumble and then purr as you eat her out, making her moan in genuine pleasure while your tongue circles her sensitive clit. "Ummm... Yeah...! I like that...!"

"Mh-hmh?" You grunt back at her while savouring the taste of her pussy, giving her a gentle slap on each of her buttocks and then continue to knead them while sliding your thumbs along the sides and lips of her delicious sex. Once you feel you've cleaned her out a little and refreshed the lubrication on your fingers you get back up on your feet and firmly push back into her again, making another moan of delight escape her lips at the feeling of your hard cock filling her moist pussy while your thumb sliding back into her ass is rewarded with a bit less enthusiasm.

This time you're fucking her a bit harder than before, finding her to enjoy the increased tempo just as much as you do despite having your thumb gently moving back and forth through her tight sphincter. You're quick to notice that she's making much more use of the muscles inside of her vagina now, increasing your pleasure and quite obviously so with the intention to make you cum quicker before you get any other strange ideas than having just your thumb exploring her asshole.

You're not falling for that simple sort of trap however, and after a while you're backing out again to cool off a little, spending the spare time to get back to the pussy-licking but this time leaving your thumb firmly lodged inside the girl's upturned ass and using it as a sort of rudder to keep her steady while you lap away at her sex. Despite showing a few signs of discomfort about your actions she's still moaning just as much in pleasure as last time from your skillfull licking, even shuddering and squirting just a little bit as you manage to drive her through a lesser semi-orgasm.

You repeat this for several times, alternating between fucking her and licking Nancy's young pussy to let yourself last for as long as possible while at the same time urging her steadilly onwards through more and more pronounced micro-climaxes until she's all sweaty and panting in heat from your administrations. Your thumb gently continuing to work her tight ass soon seem at least partially forgotten as she doesn't even wince any longer each time you pull out to re-lubricate or press back deep inside of her.

Lulling her into a sense of safety you keep pushing her closer and closer to a real orgasm, biding your time allthough you find it more and more difficult to hold yourself back from climaxing too early...

Question is: What are you holding back for? Will you be able to do so for long enough? And will she be willing even then?