Young school teacher (not beautiful but cute, shorter in size than her students, small breasted enough to be insecure about her appearance, but with a gorgeous round-cheeked ass) is asked to be faculty advisor for the school's Photography Club. The boys, mostly nerds, mostly shy themselves, need a model, and so begins the process of getting this teacher to model for them.
It begins legitimate and educational, but the boys' lust gets them to try to talk her into posing more revealing. A key early scene would be where the boys need experience with light on the rounded contours of skin. They show the teacher an artistic b&w picture of light on large breasted woman. Teacher points to her chest and says she can't help them. They point to her ass, beg awhile, and convince her that it's a legitimate way for them to develop photography skills. Once they have the teacher posing in bikinis and thongs and lingerie, they begin tricking the teacher into provocative poses and angles that produce nip slips.
I could see two ways to take the plot from there:
1 - she increasingly gets turned on by their attention and willingly goes further in her posing, volunteering peeks and slips, until she has sex with one boy, then two, then all the boys in a climax gangbang, or
2 - they blackmail her with threats of publishing her more sexy photos on a website, putting her career at risk. With that leverage, they begin to force her to pose lots of ways. Put her with a lesbian student, who begins to seduce the resistant teacher while they photograph. Bring in a big janitor or black man for her to pose next to his giant cock, which gradually goes from posing to simulated sex to actual sex. Put teacher in a bondage set. You could pretty much explore any fetish or genre from that point.
And if I was pitching this plot to a filmmaker, I'd emphasize how much of the story could be told cheapley with multiple series of still photographs, in which the teacher becomes less modest, more daring or sexy. If it works economically, he could make it into a series using this same plot, casting different looking teacher actresses: tall, short, busty, flat, slender, shapely.