Teaching science during the high school years is probably one of the most difficult challenges for homeschoolers. It seems like the popular thing to do these days is participate in a paid co-op where the parents hire someone to teach the course.
The most common high school homeschool science curricula are Apologia, Bob Jones and A Beka. All of these are written from a young-earth creation perspective. This isn't generally a problem for chemistry or physics. But it is a huge problem for geology, geophysics, and astronomy. Biology texts are usually mixed - most of the information is correct, while some of it may not be.
Christian parents need to be aware, however, that there is a movement within the university community to not accept high school science credits for courses where books by these publishers were used. Why? Because in the minds of college administrators, a percentage of the information presented in these texts has been proven false. Sadly, I can't say that I disagree with this perspective.
In general, I discourage Christian parents from participating in co-ops where books by these publishers are used in earth sciences or astronomy, and be aware of the potential risks in using them at all.
So what are the alternatives? Well, the ideal would be to convince your co-op to use a mainstream science text. But I realize that may be a challenge. Another option is to use online courses. Here are a couple that I have found:
Brigham Young University - Yes, the LDS college. BYU runs an extremely elaborate, cutting-edge independent study program and from what I can tell, it doesn't appear that their religious perspective has "polluted" the science courses. Students can even get college credit while still in high school! They also have general science courses for Grades 7 and 8 as well.
Northwestern College: NEXTSTEP Program - They have courses in chemistry, astronomy, and even biblical archaeology. (How cool is that?) Lots of other great courses, too.