For a long period which roughly coincided with the founding of America, English-speaking people only learned to read using the Bible, and often that was the only book they ever used for anything so it became a sort of de facto dictionary and Guiness Book of World Records and all kinds of things that it was never meant to be, plus a lot of new things it was never meant to be, and of course the things it was always meant to be.
Mandatory firearms training in school would be more Constitutional than teaching the Bible though. For a very important reason. Akin to a “prime directive” if you will. If you want kids to study it as an elective then fine, allow that, but forcing it on kids is wrong, wrong wrong.