It is up to schools to decide what to say about periods according to the make up of their classes.
By that very same standard, it should also be up to schools to decide to teach creationism or the flat earth depending on the makeup of their classes, surely?
Remember, some of the more fringe religious types find it utterly horrifying and insulting to even suggest that Darwinian evolution might be true. So, if you happened to be teaching a class with a significant number of kids from such families, wouldn't it be the "kind" thing to do to teach creationism or at least compromise and settle on intelligent design?
I'm not trying to be flippant. The two scenarios might not sound very alike on the surface, but in both cases individual notions of or preferences regarding reality are prioritised over all that is known about the actual facts - in this instance biology.
The insidious part is that doing this doesn't actually do much harm at all on an individual level. Maybe little Johnny or Jane will even genuinely feel better if what they're taught corresponds to their deeply held beliefs. Unfortunately, it is a harmful thing to do in the grand scheme of things to systematically undermine our actual best current understanding of reality. For a stark example, see AIDS deniers.
Biology is about us and therefore intrinsically bound to our notions of self, which I reckon is why it's so susceptible to crap of this nature. We wouldn't put up with this shit in any other discipline: e.g. it simply wouldn't occur to anyone in their right mind to teach that gravity doesn't apply to kids who just really, really wish they could fly.