It's meant to be challenged in court in hopes that that the current Supreme Court will make some subjectively favorable "clarification" about what the Establishment Clause, etc says and provide a green light to more/other policies even if it strikes down this one.
It does seem like a pretty crude attempt at that, likely frustrating to those who would have preferred to see a more sophisticated challenge raised, but that's what it is.
That very clearly isn't the goal or agenda behind what's happening in Oklahoma, however. And even if it were, the subject would be too complex and nuanced to teach to fifth graders, which is why most such courses are available at higher levels and as electives, and they don't exclusively focus on Christian doctrine.
When I visited a county fair in Texas once, somebody handed me a booklet that was just the New Testament, which blew my mind. I did not know that Christians just drop the Hebrew Bible.