Expose the equal time argument. The concept of equal time may be a praiseworthy cultural value, but it is irrelevant in the world of science. Science is not a democratic process and scientists do not decide which theory is correct by taking a vote. The key to the acceptance of a scientific theory is if it explains facts and observations better than others. Evolution explains observations in paleontology, biochemistry, comparative anatomy, embryology, biogeography and many other fields.
Creationism explains nothing.
To the average American, it seems reasonable that if one teaches evolution, one should also teach creationism because it's only fair. It is not fair to teach that the world goes around the sun, and then give equal time to the geocentrists. It is not reasonable to teach students that six million Jews were killed by the Nazis, and also, in fairness, to teach that the Holocaust is actually just a propaganda ploy of Zionists even though there is a constituency for this point of view. We shouldn't be teaching crackpot history to our students just because someone thinks it is fair, and we shouldn't be teaching crackpot science i.e. creationism either. We must teach Americans how science works, and why it is the best method human beings have developed to understand how the natural world works though it has nothing to say about ultimate cause.