I'm not an atheist but I personally believe that we should teach evolution and science because students get enough of religion by going to church. The responsibility of school should be to teach students about what's been discovered, invented, how life has evolved during the years, the big bang, etc. It's up to them as they grow up to choose what they want to believe. So my personal opinion will be to keep religion out of schools.
That's the simple answer, but it's more involved. On my BILL MORGAN'S QUESTION: Should Kids be Taught About God? page, I offer my response to a local creationist's question, "If God exists, should the kids be taught about Him?". His question was ambiguous, but he refused to clarify it while demanding a strictly yes/no answer from me, so my general answer was: "Yes to some interpretations of the question and no to other interpretations, depending on the circumstances and completely independent of whether any god or gods do or do not exist." And I explained what those interpretations could be and how I responded to each specific one. Follow that link to see that, since I personally think it was a good answer as did a third party in that conversation. The creationist was unable to understand any of it and ended up fleeing the discussion by cancelling his email account.
The first point of confusion is differing definitions and goals of "teaching". In religion, the goal of teaching is indoctrination, dictating what the students are required to believe and then compelling them to hold those beliefs. In public schools, the goal of education is not to compel belief, but rather for the student to understand the subject matter.
Obviously, we would not want public schools to engage in religious indoctrination, but that should not prevent teaching about religion in public schools. In social studies, history, art, and literature we should teach about the various religions so that the students will know about the beliefs and the history of various religions, the religious factors in a multitude of wars, and the mythological themes from all religions that appear repeatedly in literature and in works of arts (we already do it for Greek and Roman mythology, so why not the other religions?). So long as you do not try to compel the students to convert to those religions.
The proper subject matter of science classes is science. However, there can be value in mentioning old discarded ideas (eg, geocentrism, caloric theory, phlogiston) and showing why those ideas are wrong. There can also be value in looking at instances of pseudo-science and showing why they are wrong. Most of that should be doable in less than half of a single lecture. This could be the proper role of creationism in a science class.
Unfortunately, this reasonable approach can present problems. First, it must be implemented in good faith and we know from long bitter experience that religionists almost never act in good faith, but rather would certainly result in them trying to subvert and exploit the system.
Another problem with teaching about religions is that those religions would end up trying to prevent that teaching. For example, Mormon parents would certainly rebel at their children learning the actual history of the origins of Mormonism.
So the issue is a bit more complicated and there are good reasonable solutions that should be satisfactory to all parties, except for the fact that not all parties will be reasonable.