By my understanding, education is a state responsibility meaning the Feds can't force an issue to be taught. Yet the states' education systems are subject to the constitution and can be prevented from teaching certain things. Feel free to correct me if I'm wrong there. I'm not American so I'm honestly not sure how it works.
Personally, I don't think that intelligent design should be taught in schools and I do think evolution should be taught as a theory, which it is. The problem with intelligent design is that it observes certain relationships in the universe, but rather than try to examine or explain the phenomena, intelligent design proponents jump prematurely to a supernatural explanation. The three great problems I see with this approach are:
1) There is no attempt to study or explain the phenomena as observed. By and large, this study is conducted as molecular chemistry and quantum physics. The jump to a supernatural conclusion before these and other fields of scientific research have rendered a conclusive verdict is premature.
2) The supernatural conclusion reached by our intelligent design friends always seems to mean God, more specifically the Judeo-Christian God. It leaves out all equally plausible and implausible alternatives. If or when science fails to explain our universe, then and only then should we be considering explanations beyond our scale, dimension, or ability to comprehend. It is a conclusion that requires a priori faith in the answer.
3) Intelligent design cannot be science, period. Science by definition provides an answer based on demonstrable, provable and repeatable conclusions. Intelligent design provides a solution that is none of those things, therefore cannot be considered science.