Very convincing if you are preaching to the choir. when the school authorities make claims about scientific theories that scientists do not share, in science textbooks, the claim that this is not part of the science curriculum is, well, coy. If you wish to make this claim in the cafeteria, in an informal discussion, maybe it's not a constitutional question. If you choose to insist on labeling science textbooks with claims that support your religious beliefs, and the judge uncovers the fact that your motivations are, in fact, religious, and your claims do not have the level of scientific respectability of dozens of other pseudo-science claims no one in their right mind would dream of putting as a label on a textbook, there is nothing, that makes sense to me, to shield you from the critical eye of the keepers of the Constitution.
You seem to think motivations are actionable. Treading very near the edge of thought crimes don. Perhaps you should reconsider since Scalia agrees with me that motivation, absent action, is dispositive of nothing.