OK, creationism is a valid subject in a school curriculum, when teaching about the history of scientific theories. You just can't start off with the theory of evolution, and then move on to Darwin and the Theory of natural selection.
You need to explain what people believed, and what was going on at the time, and what new information came to light.
Most people accepted the biblical theory of creation, then people began to plaster the walls of their homes to keep out the cold drafts, and this created a demand for gypsum, and the best gypsum was found in France, near Paris, the world famous "Plaster of Paris". During the quarrying of all this gypsum, all kinds of skeletons were uncovered of creatures that didn't currently exist.
This was when the idea of evolution, that creatures changed over time began to set in.
Now how can you tell that story without explaining that people believed in the creation story of the bible as fact, before these discoveries, and that these discoveries changed peoples thinking. By the time Darwin came along, evolution was accepted by most learned people as fact, people also knew that by selective breeding they could change the characteristics of plants and animals, what Darwin supplied was a theory of the mechanism of evolution, natural selection.

Just like a history of chemistry might start off with the idea that everything was composed of earth, fire, water and air, and from there go into alchemy and from there the experiments that brought us to our current understanding of chemistry.

Without the starting point, the idea that every species had been created exactly as it currently appeared, and then the empirical data that changed the thinking into the idea that species changed over time, and then the mechanism of that change, and then the chemistry of that mechanism, the story is incomplete.

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