When I was in SEMINARY, not 12th grade, a group asked the administration for a class such as this and we were told that it wasn’t appropriate in seminary, but should be left for when we were kallahs.
That said, I think that what you want to know is something mothers should tell their daughters, whenever they think it’s appropriate, as part of telling them about the beauty and kedusha of intimacy. And I would say that it’s fully appropriate for a mature young woman to do her own reading, such as R. Kaplan’s Garden of Eden, to be literate in important hashkafa and general knowledge. But generally, the nuts and bolts should definitely be reserved for kallah classes.
By the way, this could segue into what’s appropriate for high school, what should be for seminary, is sem. necessary, etc.