Evolution is about as close to a 'fact' as humanity can possibly reach. We can't really know anything for a 'fact', as in there is 0 possibility of it ever having turned out to be the contrary, so our definition of what constitutes fact is not purely absolute. Holding evolution to an unobtainable standard makes no sense. Evolution is about as solid a fact as we can get, but that doesn't mean that we can't later find out that we were wrong (which is about as likely as God coming down from Heaven and giving me a high five). Basically, unless you're willing to deny that gravity is a fact (something any reputable scientist would be loathe to do), then you can't strip the title of fact away from evolution either, since both concepts are both theory and fact.
Intelligent Design should not be taught because there's nothing to teach. What the hell are you going to say, "look around you, surely something must have designed this in a reasoned and coherent way, it can't simply have been the product of a random chain of events...class dismissed"? There isn't really anything substantive to the theory of ID that makes it worth teaching. In fact, it's so intuitive that it doesn't even need to be taught, especially since it's not hampered by the need to be supported with evidence. It's not science. It's not math. It's not even rightly regarded as philosophy at this point. Where are you going to teach it, in a creationism class? Just because something has a theory connected to it doesn't mean it needs to be taught. Do you have any idea how many theories about the origin of the universe are not taught in school? What about Scientology? Scientology has about as much scientific standing as ID, so if ID should be taught in schools, so should the principles of Scientology. It also has about as much proof to support its claims.