I think you forgot the scenario, so here it is in more detail. Please rewrite using this.

A female 8th grade teacher was teaching sex ed to her students. During the lecture the teacher decided it would be best for someone from the crowd to be used as an example for learning the vagina.
Write about how a smart girl came to the desk, spread her legs and the teacher started showing the class on her the diffrent parts. Once in the lecture she put her finger in the student to spread it and show the inside and the rest is your imagination.