The problem with this is that their are an infinite number of possible "theories" using your definition of the word. Evolution is the only evidence supported theory I am aware of that describes the mechanism by which living things change over time. If we were to teach creation (which attempts to explain A LOT more than evolution does) we would have to also teach every single hypothesis that was ever developed to explain the origin of the world.
Yes, even including the flying spaghetti monster.....
The answer is NOT to teach Intelligent design. I think the answer is to include a simple lesson at the beginning of each science class.
1. Science DOES NOT prove things
2. Scientific theories are NOT truth, they are simply the best explanations we can come up with to fit the available facts. They are subject to change at any point
3. Science is not about belief. In fact belief is completely irrelevant to science. Your computer will continue to work whether you believe in the free electron theory of metals or not. Gravity will continue to operate whether you beleive in all aspects of the theory or not.
4. Science does not disprove religion or god. In fact god is IRRELEVANT to science. Science does not care whether a god exists or not and has nothing to say in the matter. Science is not an attempt to disprove god, it is an attempt to explain evidence we find in the world around us. Nothing more, nothing less.
5. Everything you learn in science class is simply the current understanding we have concerning the way the world operates. Our understanding may/will change in the future and that is key to the whole process of science