Here is the study that was done for the PLoS Biology journal on creationism and evolution in the classroom. The authors write, among other things:
We followed most previous studies in asking teachers to think about how they allocate time over the course of the school year. We went a step further in also asking whether evolution serves as a unifying theme for the content of the course. Over the entire year of high school biology we found substantial variation among America's high school teachers (see Table 1).
To me, more interesting is Table 2:
Even though there is clearly a strange thing going on with biology teachers, there is also a huge gulf between the biology teachers and the general public. Read the article.