Competing scientific theories - fine, but Creationism hardly fills the bill. Besides, the question is about public schools. Is any high school student sufficiently based in science, especially biology, to do more than a cursory examination of anything? I think not.
Why not examine the evidence for creationism with rigorous scientific principals? I'm not suggesting that creationism be presented as truth, just examined as science. It should take all of half an hour to debunk creationism. If the point is to teach student how to think, then what are you afraid of?
Besides, the question is about public schools. Is any high school student sufficiently based in science, especially biology, to do more than a cursory examination of anything? I think not.
Expect little of your students, and that's what you will get.