Story is probably from the 70s or earlier. Maybe a short story, but I cant be sure. I stopped reading horror stories. (The Amityville Horror novel freaked me out big time and that was about the last horror story I ever read)
I was reading a recent webtoon with a monster who was killing students in a school and the teacher tries to stop it and was killed too, and it reminded me of this story.
In any case, the story was set in a very small town, (maybe with the classic one room school, with an old female teacher, who has been teaching there for many years.) Some of the older female students in the school are being sexually assaulted and killed. If I remember correctly, the police/sheriff/news/gossip was saying that the object they were assaulted with was the diameter of a 4x4" or 6x6" and whether that assault is what killed them, or were killed after the assault I don't remember for sure, but I think they died during the assault due to the size of the object used.
This is a horror story, not porn, and there were no scenes of the assaults in the story. Just vague descriptions of the discovered bodies, and the rumor mill gossiping about what was done.
I think 3-4 girls had been killed at this point.
I believe, one of the male students had been possessed by a demon, or was a monster in disguised, or had a "pet" creature and was looking for a pure students to procreate with/get life essence from/gain more power? He knew one of the girls in the class was a pure and had been arranging to meet them after school, and after transforming into the monster/summoning the demon/calling the creature over, the creature could sense or smell, that the girls were not pure and did it anyway with his tool which was that large, and killed them.
In the end, the teacher figures out who the male student is, based of the victims and his interactions in class with them, and who is the most likely the next victim. That girl is at the school after class studying/cleaning/hiding and the teacher runs to get her out of there before the male student gets there. (She may have called the police/sheriff also.)
Unfortunately she does not get there quick enough. The male student is already there, has the girl pinned down, and is transforming/summoning/calling the monster.
The monster arrives, and knows the pure subject is there. But, just as quickly realizes the student is not pure, and the only other girl in the room, is the old spinster teacher. So it releases the student and heads toward the teacher.
It is only at this point the readers understand why the victims have been chosen, that the monster is looking for virgins.
The monster is then killed. How? I don't know, whether it was she threw some chemistry subject chemicals on it and killed it, or knew it was allergic to some substance and threw it on it, or the police/sheriff arrived just in time and shot it, I don't remember.
In the last few lines of the story, the teacher is thinking she is never going to tell anyone the monster was after virgins, and that she was a virgin, which is why the monster left the girl and switched to attempting to attacking her, that's nobody else's business. (She might have been calling herself Mrs. Teacher for many years so everyone thought she had been married, but she never was, and had never done it.)
