I would atleast teach creation because it's the opposing view that most people are going to come into contact with. I would rather people knew of the Big Bang and Evolution and Creationism than just know the Big Bang and Evolution and then be ignorant to the views of other people.
It's not like it would take more than a lesson to teach it.
It's 7 days of God creating the world and then a Garden of Eden story.
Creationism is any religion about a god creating the known universe or creating things that created the universe. That means Christianity, Catholicism, Islam, Judaism, Greek Mythology, Roman Mythology, etc.
You can't just teach one.
Also, the bias of the teacher could affect the teaching even more than it does now. (e.g creationist teachers underplaying evolution and vice versa)