There was a good article on evolution and intelligent design theory today in the Washington Post: "New Analyses Bolster Central Tenets of Evolution Theory"

Give it a read. It lays out some of the recent tests (working with the chimp genome, differently evolving bacteria colonies, etc.) that support evolution.

One of the article's main points is that evolution is testable. It is science because you can make predictions, set up experiments, and see if the results of the tests support your theory.

'Intelligent Design' shouldn't be taught in science classrooms because it isn't science. It's not testable. Furthermore, ID makes a lot of claims about evolutionary theory that are just wrong. The central tenets of ID... their ideas about irreduceable complexity, and the idea that evolution can't account for dramatic changes in morphology are based on very simplistic notions that don't take into account the modern understanding of how evolving animals make small changes to existing 'programs' and resources to achieve what appear to be radically different designs.

...

Anyway, the teaching of evolution (or not) will have all sorts of practical consequences for future scientific advances. Besides being crucial to understanding genetics and bio-engineering, evolutionary concepts can be applied to other fields, like artificial intelligence and nanotechnology.