Since my academic background is primarily in public policy, I'm going to stay away from the scientific jargon as much as possible. What I would like to do is discern the issue from a public policy standpoint and determine whether theories such as creationism and Intelligent Design (ID) should be taught in schools.
Before answering the question, I should first specify the sort of schooling towards which this questioning is targeted. This is not geared towards homeschooling because in spite of accreditation requirements, parents who homeschool their children have more latitude in what they teach their children (As a side note, I am interested by the fact that even with the disproportionate amount of home-schooled children being Evangelical Christians, there is a growth of secular, home-schooled children). Similar arguments can be made for private schools, and to a lesser extent, charter schools. This primarily leaves us with the question of whether these theories should be taught in public schools.
This leads us to the next question of "what is scientific theory?" When used in the world of natural sciences, the word "theory" does not mean "a set of ideas that are presented to explain something, but may or may not be true." When we say "scientific theory," we mean to say "a well-substantiated explanation of natural phenomenon that can be confirmed through observation and experimentation via the scientific method." I remember when I was in college, I took a course of the physics of light, and there was a lot of debate as to whether light was a wave, particle, or a combination of both. Even with the debate, there were still a set of high standards that was applied to the scientific inquiry.
Now that we have a better grasp of "scientific theory," let's move over to the differences between Creationism and Intelligent Design. Just for the record, these are not synonyms. According to Webster's dictionary, Creationism is "the belief that G-d created all things out of nothing as described in the Bible, and therefore the theory of evolution is incorrect." Creationism is a sectarian ideology based on biblical literalism, a literalism that I find to be irksome. Creationism is not taught with secular intent. Creationism should be left for Sunday schools, not for public schools. Doing otherwise would be a violation of the First Amendment.
Intelligent design, on the other hand, simply states that an intelligent, powerful being created the universe in a directed process. Note that the theory of intelligent design does not postulate who the designer is. It could be G-d, الله, or one of the deities from polytheistic religions. Heck, it can even be the Flying Spaghetti Monster, and it would still be a form of intelligent design! The notion that the universe was created by design, rather than random mutations, is not an argument that inherently religious in nature. What's more is that there actually is a cogent case to be made for "design in nature," whether it comes in the form of the fine-tuned universe argument, cosmological argument, or the specified complexity argument. To secularly argue that there is intelligent design has a lot more validity than arguing that the world was literally created in six days and that the world is literally about six millennia old.
Before I go into the policy analysis, just a few words on how I personally feel on the matter. Unlike most of America, I do not find a dichotomy between science and religion. Science explains the "how," and religion explains the "why." Let's say that natural selection and random mutations are undeniably the mode through which we came into being, which based on discerning what I can from the scientific evidence, it's the most probable scientific explanation. I don't care because it does not violate my understanding of Torah in the slightest, and it does not shake my belief in monotheism because evolutionary theory and Judaism are not mutually exclusive. There's no contradiction in me being a theistic evolutionist.
In an ideal education system, I would like for school to be an institution in which students can openly discuss and debate varying points of view in a respectful, civil manner. This is why I am certainly not going to advocate for removing evolution from the classroom, but I'm also not going to say that evolutionary theory is as "open and shut" as one would like to think because it's not. With regards to this particular topic, the debate is framed in terms of "science versus religion," which is problematic. Creationists like to view their opponents as g-dless, condescending heathens, and evolutionists like to view their opponents as Bible-thumping troglodytes. Until people frame the debate in terms of "Was nature created by design or randomly," we're going to be stuck in this uncouth stalemate that perpetuates the idea that there is nothing in between atheistic evolutionist and creationist that would actually create a spectrum of viewpoints on the issue.
One of the simpler solutions, which evidently has a libertarian twist, is to get the government less and less involved in the education sector. A competitive market in education might not have answered the question of "Was nature created by design or randomly," but it would have mitigated the political tension by now. At the very least, we can think about policies (e.g., tax credits, school vouchers) that could allow for lower-income families to have better access to the education marketplace. Although there is some potential for allowing additional privatization of education, it would be relatively more prudent to figure out what to do with the public school's current K-12 curriculum.
Even if I am a proponent for more privatized education, we should still aim for a higher standard of intellectual discourse in our public schools as long as the public school system still exists. What could be done is seeking out some schools willing to pilot a science curriculum that can teach biology, as well as present cases both for evolutionary theory and intelligent design in a relatively fair, unbiased manner with supporting evidence for each side. If it's a success, then other public schools should take a cue from its success and implement it themselves. With that, we can theoretically preserve the First Amendment without having to quash intellectual debate (more on that below). It would be great to see ID taught in a secular fashion, as well as a reasonably objective one. However, I think this would be asking for too much with a country that is so divided on the issue. Not only that, an issue I find with the theory of intelligent design is that it does not meet the standard of falsifiability, which could arguably put ID out of the realm of the scientific method because even if there were unquestionably a designer, who is the designer responsible for the universe's creation? The interplay between evolution and how it relates to religious beliefs can be debated in a social studies or politics classroom. This alternative would allow for the discussion to be had, but to "leave science in the science classroom," which would a compromise from my view, but something tells me this would not be an acceptable policy alternative for creationists.
I am thinking that in an American context, tweaking the curriculum without altering it greatly would work best because my main concern is that ID would be used as a gateway to advance the agenda of creationism (see Epperson v. Arkansas). With that in mind, if only evolutionary theory is to be taught in the science classroom, it should at least be taught with a presentation of its strengths and weaknesses, as opposed to being unquestionable dogma, so that students can understand evolutionary theory from all angles and allow for enough intellectual wiggle room in the event that evolutionary theory is incorrect. Although part of an education is teaching facts, the other part of an education is to enable students to think analytically and be able to problem-solve, which this latter policy alternative would permit. This curriculum stipulation would allow for students to think openly and critically while not having religion shoved down their throats or freedom of inquiry stifled. Given the political climate, this would be the best policy alternative to the status quo.