Plenty of science that is theory is taught in schools so you believe teaching one theory is OK apposed to another. I have no problem with both being taught personally.
Actually,
all of science, one hundred percent of it, is theory.
In science (and everywhere else the word is correctly used), Theory (as well as Principle and Law) represents established, evidence-based explanations accounting for currently known facts or phenomena, or for historically verified experience. Theories make predictions, predictions that must be true if the theory is correct, but also predictions that can be falsified, which in turn proves the theory in incorrect, and thus either dismisses the theory, or the theory must be changed to match the evidence. The predictions these evidence-based accounts have been well tested by experiment and observation. Examples include the theory of relativity, the law of gravity, the germ theory of disease, the principle of conservation of energy.
The big bang theory, for instance, predicts certain things, one of which is the temperature of the background radiation left over from such a cosmic explosion. This prediction was made long before science could even figure out how to make such a measurement. Many years later they figured out how to measure the temperature, and it was exactly as predicted. Does that prove the Big Bang Theory? No, it doesn't. But just as importantly, it doesn't disprove it, so the theory stands until something does. Every scientific theory is exactly like that, a theory, waiting to be proved or disproved, by observation and experiment.
Creationism isn't science, it's belief. Intelligent Design isn't a theory, it's a belief (albeit one that has been proven to be just flat out made up, specifically as a means to get creationism into the biology curriculum in schools). Neither one makes predictions that can be falsified, which is the bedrock of all scientific theory. Instead, you are expected to take it at face value as true, and if you don't take it at face value, then they have other non-falsifiable ideas they'll put forth as evidence to it. So what it comes down to is, both the terms "theory" and "evidence" are being used incorrectly, co-opted for the purposes of advancing an agenda. Creation Science is an oxymoron, because it's sole piece of evidence is a book that doesn't allow falsification. Creationism isn't a theory, no matter how many times you call it one.
There are two primary differences between a between a scientist and a creationist. One is, a scientist has the courage to say, "I don't know." The other is, a scientist will accept evidence when it differs with his personal beliefs. If you can't do either of those things, learning stops.