How-to sex guides and the like are not appropriate for a high school library.
> To go further, almost everyone agrees that a cartoon of a man and woman having sex in the missionary position for the purpose of procreation is not necessarily pornographic; this is a standard sort of picture in age appropriate sex education materials.
Is it? I don't recall having been shown anything like that.
And I would say a cartoon of two characters having sex and showing penetration would necessarily be pornographic. A medical illustration wouldn't (think stiff, cutaway diagram, narrowly focused on the necessary parts), but that's not a "cartoon."
> Granted, these images concern sexual reproduction. However this only makes me question why people deem that image appropriate, but images of other positions or acts not worthy of learning about in other contexts.
I think you need to figure out the difference between sex education and a sex guide on your own. You're playing fast and loose with categories, and getting yourself tied in knots as a result.