"NAME_1 and his friends NAME_2 and NAME_3 talk NAME_1's younger sister NAME_4 into flashing her teacher during biology class. After class has begun NAME_4 slides down in her chair and spreads her legs, revealing to Mr. NAME_5 that she is bare below her school skirt. Indignant Mr. NAME_5 makes her sit on his desk facing the class and repeat her performance for a special live biology presentation while he slowly unbuttons her uniform blouse. NAME_4's classmates form a half-circle in front of her and study her physique in detail with Mr. NAME_5's support and guidance. Some boys secretly take photos while NAME_4 is presented and explored."
Flesh the story out from here, make it smutty. Focus on the presentation part with a passive and embarrassed NAME_4 on display and an unusually curious and engaged class.