She wants him. Yes he's older with silver in his hair and is a little short, but she hasn't talked to a boy--let alone a man--in so long. At 18 years old, her body and mind are very much focused on one particular thing.
She tries to hold back at first, just be the helpful girl when he substitutes in her classes; the rest of the girls are practically mean to him, like they scent weakness, so she wants to make up for that with kindness. If her mind goes rather quickly into the gutter, well, at least she tried, right?
When he stands at the lectern, she wonders what his cock looks like, if it's pressing against the zipper of his pants, if that's what that bump is.
When he writes on the board and his ass wiggles ever so slightly, she daydreams about him pinning her to that board with his body, grinding up into her cunt with enough force to push her up and slide down before he once again drives in.
She starts to crave his presence, and when he is in class, she attempts to seduce him. Slowly at first, of course, so he doesn't catch on until it's too late and she has him.
It begins with the little things, like unbuttoning her uniform blouse just a little lower than dress code allows. The first time he notices, he's standing in front of her and her geometry group's low table, answering a question, looking at them from above. His gaze shifts to her, and he is abruptly silent, eyes locked onto her exposed cleavage, meager as it is, and his cheeks and nose turn pink.
She can't let him know how smug this makes her, so she looks down as if wondering if there's something on her shirt, gives a fake gasp, and clutches the sides of her shirt together as if she's horribly embarrassed by a wardrobe malfunction. The sound brings him back to the room, and he immediately turns and walks away to another table of students.
Bolstered by her success, she decides to kick things up a notch. When her Religion IV teacher--of course it would be religion class--lets the class know that there will be a substitute the next day, she is determined to catch his eye again. The following day she has her blouse unbuttoned again, her plaid skirt rolled up just a tad too high, and she's wearing knee socks into smooth, lowly heeled, barely regulation women's loafers. With a simple black choker on her neck, a smoky perfume on her wrists, and a soft, shimmery gloss on her lips, she sits down at her desk in the very back row and waits.
He makes his way to the lectern, and she crosses her legs into the aisle to give him a glimpse of their length and smoothness. Once he's started reading the scripture passage for the lesson, she takes her pencil and slowly runs it down her neck to her collarbone, subtly squirming like she enjoys the feel, though her face is serious. She looks at her desk as if she's intently listening while he goes through the longest list of names in the genealogy of Christ, but she's brought the pencil back up, now running across the seam of her lips in purposeful absentmindedness.
All of a sudden he is saying her name in place of one in the list, and she looks up in honest surprise that it worked so quickly. He resumes reading out loud while the whole class turns back to look at her. With wide eyes, she shrugs and shakes her head as if she has no idea what's going on.
The next time she sees him isn't until a week later during study hall. Apparently the school librarian is out for the foreseeable future with the flu, and he was the closest to a librarian the school could scrounge up on such short notice. Once her bag and notebook are at her usual table, she offers to help him put away the returned books. They go about this separately at first, but eventually they have books on adjoining shelves.