I just went over this travesty of a story and could only find three things I would change.

First - when she got off of his toes you indicated blood rushing to his extremities. Um, his blood ran back to his arms and fingers too? Try another description so it works better. Maybe something like "pain filled digits" or something.

The next thing was "students that" and it should be "students who", if I am not mistaken.

The last thing was "You’re worthless as a teacher, and it is making me look bad.” Considering the previous contractions the "it is" doesn't feel natural.

Otherwise, as Mad and Lews have said, this is a good piece.

As for publishing it in the library, it is a sad day when a piece of erotic fiction requires sex. Sex is not a requirement for BDSM, nor this a sex site. It is a site for erotic fiction with a BDSM twist. I say damn the torpedoes and full speed ahead. Ignore the asswipes who say you need sex and pay attention to only those who can appreciate a well-written tale.

By the way, when you first got here I was waiting for you to cross the line. You kept coming up a bit short in your offerings and I got a bit frustrated with waiting. You were just one step shy of finding what you needed to be quite good. You crossed that line quite well, snatching the stone from my hands with the dexterity of a bald headed white kid posing as a Chinaman. Or, as Lews said, ya done good.

Now, gimme back my rock!