I strongly believe that as it is the overwhelming scientific consensus, and there is a lack of rational opposition to it, it should be taught as fact until the event that a better theory comes along. This is the nature of science. Religion has no theories, in any meaningful sense at least. As a theory, evolution is based on hundreds, if not thousands, of scientific tests, and we can be reasonably sure that it is the most accurate theory. This does not mean that if the scientific consensus changes to another theory as the one with the most evidence supporting it, it would be foolish to stick to evolution, as that is more the nature of religion than science.
No observation of macroevolution ( when a species turns into a new one) has been observed. This is briefly documented by citing recent statements from leading evolutionists admitting their lack of proof. If evolution is a real process, then how come we have no recorded observations of it happening. Current leading evolutionist, Jeffery Schwartz, professor of anthropology at the University of Pittsburgh, has recently stated: "... It was and still is the case that, with the exception of Dobzchansky's claim about a new species of fruit flies, the formation of a new species, by any mechanism, has never been observed." Though I am religious, don't automatically count me out. I was taught and I do believe in respecting other's beliefs and ideas. That is exactly what evolution is. A belief and/or idea. I do believe it should be taught, but not as a fact because we have no absolute proof of this. Only theories.
There is no adequate proof of the origin of life. an evolutionist would believe in beginnings. But we all know life doesn't come from nothing. And something everyone should know is that Darwin based part of his theory on spontaneous generation. Our fossil record is our only documentation of whether evolution actually occurred and it lacks any transitional forms, only fully formed when first present. So again. There is not very good proof of evolution. So why should it be taught as fact.