First, please familiarize yourself with this article from PBS NOVA:
Just as it says in the article's intro, I too was shocked it still goes on. I mean I know it's unpreventable in certain remote areas and certainly in private schools, but I didn't realize how much of a hold religion has on public classrooms. The article cites a 2007 survey (I know, not exactly fresh data) of biology teachers and evolution. It found:
-13% endorse creationism in the classroom.
-21% call creationism a valid alternative to evolution.
-22.4% spend at least an hour of class time on creationism.
Religion is of course something everyone is entitled to. But it is not scientific. Evolution, on the other hand, is fundamental to our understanding of how not just humans but all life came to be on this world. From the article:
"So we can conclude that somewhere in the neighborhood of half a million students will be presented with a favorable view of creationism/ID this year in their high school biology classes alone.
That's a lot of students being misled about biology's central organizing concept."
Do not be too hasty however to blame teachers. Many may be feeling pressure to "present both sides" as Americans supporting evolution-only classes are in the minority. Nearly 60% support teaching creationism alongside evolution.
The Catholic college I teach at has its own approach. We thoroughly teach evolution and of course the view that it is God's means of creation. This is much different from "creationism" which states an invisible man twinkled his eyes and all life came about in less than a week and the allied psittacisms of Sunday schools. One has evidence. The other does not.
Teaching evolution is not a matter of science versus God. Evolution does not obviate God nor can I imagine an almighty enraged by our study of the fossil record or seeing it as "devil's work."
Do we really wonder why many Americans lack a basic understanding of scientific principles? I'll give you a hint as to why.
It's not because of teachers.