Homework under Sarah's desk

"Well Doug I got some homework to do so why don't you be a good boy and get under the desk and get a treat," Sarah said backing up from her desk giving you room to crawl under it. You were unsure having homework yourself and knowing if you went under the desk it would defiantly cement your place as your little sister's cock slut. "Well I am waiting," Sarah said, you were still turned on as Sarah pulls out her cock and lets it hang, your lust makes up your mind and you quickly knell down and crawl under the desk. Sarah allows you to turn around before pushing herself in and placing her cock right in front of you. You reach out and touch it but Sarah pulls back and looks down at you, "Now Doug you must restrain yourself until I am done with my homework. If you cannot do that then I may have to punish you."

For a moment you were thrilled at how she would punish you but you did not want to upset her, "Yes Sarah I can restrain myself."

"Now there is another way you can help out you can work with me if I have any problems so this can go faster," Sarah said petting the top of your head making you feel proud.

"Sure thing Sarah," you say and she smiles at you and pushes back into the desk. You were aware that Sarah would most likely not need your help as she was top of her class so you just sat there watching her cock swing back and forth. After a few minutes Sarah starts to fidget which unfortunately meant she was swinging her legs and gently kicking you. You tried to show some restraint knowing this had to be some sort of test but after about ten minutes you can't take it anymore and grab one of her feet and...