bymeidel, while i agree to some extent with your concern, i honestly think that theres a time and place for everything, and 12th grade is not the place to learn about hilchos niddah. i further find it hard to believe that any scenario whatsoever never came up in your BY education. when i was in 12 grade, we had a segment of our curriculum dedicated to “family life” topics, that touched on just about everything–but TOUCHED!! opened our minds, gave us insight, and the rest was left for a more appropriate forum.
on another note, not everything is appropriate for a classroom discussion: if you are curious, ask a rav, or better yet, your mother, or ever better, wait till kallah classes.
im the last one to tell you that girls should be in the dark until they are kallahs–dont get me wrong. i just think that a classroom is not the place, be that in HS or sem. theres room for discussion, etc, and its important you receive a strong hashkafic background. but detailed halacha classes dont sit right with me….i think its somewhat a lack of tznius….i dont know, this is just how i feel.
a part of this demands some common sense, of what is appropriate to ask, to read on you own, and when to do so.