Scientific American http://www.sciam.com/article.cfm?id=the-latest-face-of-creationism recently had an article illuminating the intent behind such policies.
A couple choice quotes:
"The real purpose of the law-as opposed to its ostensible support for academic freedom-becomes evident on analysis. First, consider what the law seeks to accomplish. Aren't teachers in the public schools already exhorted to promote critical thinking, logical analysis and objective discussion of the scientific theories that they discuss?"
"Thus, despite the lofty language, the ulterior intent and likely effect of these bills are evident: undermining the teaching of evolution in public schools-a consequence only creationists regard as a blessing."