If you’re going to read anything today, you should read Amy Harmon’s article on teaching evolution in Florida. I haven’t taught high school, but I’ve had similar experiences teaching evolution in an introductory level college course.
Evolution shouldn’t be this hard a subject to teach, but it is. It could be worse, of course. Keeping it from getting worse is the reason we spend so much time trying to deal with the narrow-minded bigots who fight so hard to keep our children in the dark.