Dolly comes to visit you after class, and tells you all the rumors she's heard about you giving out D. She knows for a fact, none of those other girls who you've given a D to would take it as good as she could take it. You tell her that if she wants a D, she's going to have to earn it. Reluctantly, she tells you she knows she's not going to be getting any better in your class, and asks what it is she can do to earn the D she wants so badly. That's when you assign after school ass stretching and cock sucking sessions. She starts by turning around, pulling her panties to the side, and sucking on the cold buttplug you gave her. She relaxes and starts to push it into her tight little hole. Once she gets it in, you can see the excitement on her face when she thinks she's finally earned your cock. You tell her, she can have your cock, but you won't be fucking her. Confused, she works out the little word puzzle in her brain realizing that means she can suck on your cock. She doesn't even mind that you won't fuck her yet, she's just happy to get her hands (and mouth) on your dick! She takes your cock into her warm, wet mouth, swirling the head around with her tongue. She drools, she gags, goes crosseyed, and loves every second of it. She asks if she's being a good student, she just wants to know she's really earning that D. She leans back, pulls her shirt up, and rubs on her pussy while her butt is still plugged. You end todays session and take your cock away. Even though she's sad not to be sucking on it anymore, she lets you know how excited she is to continue. So excited, that she even takes this tiny plug out, and shows you just how eager she is by putting the next size plug in! She thanks you for being such a good teacher, and tells you she can't wait to see you for detention tomorrow!