Let’s try the converse, shall we? The Science teacher, as state actor with a compelled audience, teaches that evolution is anti-religious. Is there a constitutional problem with that?
To say that some action is anti-religious is to suggest that it is driven by some anti-religious motive. What specific anti-religious motive must necessarily attach to the teaching of Darwinian mechanics? It it not plausibly being driven by other non-anti-religious motives?
I would agree that people who teach evolution sometimes push such teaching in anti-religious direction. Generally, though, the problem isn't with the teaching of Darwinian mechanics, but rather with teachings that go beyond that.
The basic principles behind Darwinian mechanics are sound, and are applicable in many fields for predicting the effects of various actions. Further, they can offer a plausible explanation for much of history and pre-history, though not for all of it. The only problem, though I'll admit it's sometimes significant, comes when it is presented as being the sole explanation for everything. The remedy, though, is not to attack the teaching of Darwinian mechanics, but rather to ensure that teachers make clear the distinctions between what things are reasonably certain, what things seem likely, and what things are essentially guesses.