Creationism is not science. This may seem axiomatic to most of you, but I've always found it very surprising how many people that accept this view have trouble defending it against those who think creationism is science, as valid as evolution (which is, after all, just a "theory"). Can you explain why creationism should not be taught in public schools? In a way that can't be talked around easily?
I'm here to provide you with a simple set of tools to argue rings around the wacks that will try to impose their particularly cracked view of both science and religion not on you, but on your kids. So listen up people. It's us against them, and right now they're the only ones paying attention.
Ok, the main problem is that so few of us really know what science is. I know I didn't until I was well into college, and I was the geek everybody went to in high school. Pop quiz: explain how science works.
Not as easy as you thought, eh? At its root, science is simply a way of explaining the way something, anything, works. First you watch how it works (observation), then you come up with an idea that explains everything that you've seen so far (hypothesis). However, it can't just be any sort of idea! This is the really crucial part. Your idea must make some sort of prediction about stuff you don't already know, ones you can test (prediction). If the tests fail, your idea must be wrong in some way, and if they succeed then your idea is right. The more tests you can think of that your idea passes, the more you know you're right (unless you're my wife, in which case you're already right and it's the universe causing the problem). If your predictions aren't borne out by these tests, then it is wrong either in part or in whole. It's especially useful if you can tell your friends about these predictions and tests and they can perform them and get the same sorts of results.
We all do this every day without realizing it. You come home at night and flick the light switch on the wall. Nothing happens (observation!). You think that maybe the power is out (hypothesis!), so if you look at the VCR in the living room it shouldn't be on either (prediction!). So you walk over and look (experiment!). If the VCR is still blinking 12:00 am, then your idea, your hypothesis, is wrong, because it failed to predict something you didn't already know. If the VCR is dark, then you know you're probably right, because your hypothesis successfully predicted the results of an experiment.
That's all well and good, you may say, but how's it going to help me keep that wierd old white guy in the cheap blue suit from successfully thumping his bible into my kid's homework?
The key points to keep in mind are prediction and falsification. If a hypothesis explains what is observed but makes no predictions, it's not science. If a hypothesis can't be proven false, it's not science.
Creationism fails on both accounts. Because it was created as a kneejerk reaction by people who at best lack imagination and strength of faith, it only really explains what has already been observed. It makes no predictions about things that aren't yet known, and therefore it cannot at any point be proven false (or true, when you get right down to it). It is not, at root, science.
Evolution is science. It was created by first observing the world around us, makes predictions that can be proven false, and suggests experiments that can be followed to do so. It is, therefore, science.
Please note that nowhere in this am I arguing which one is right (Creationism is in fact wrong, but that's a different story). I'm arguing about which one is science. Creationism is, like everything else created by fundamentalists (of any sort), both bad science and bad religion. By making no falsifiable predictions, one cannot create experiments that prove it to be right or wrong. It's really that simple.
And that's why it has no damned business at all in a science classroom of any sort.
Want to learn more? The world's best source of information on all this stuff can be found at the talk.origins archives. It's got everything you need to hand a creationist's or fundamentalist's head back to them ninja-style if they try to get into an argument with you. Highly recommended!