The reason public-classroom instruction varies so much, Branch says, is that teachers have many opportunities to personalize what they teach to students. State standards differ, and local school boards develop curricula that are designed to meet those differing standards. Teachers take those curricula and develop lesson plans. Then they go off into their classrooms. Do they teach exactly what’s in the lesson plan or tweak it? It’s hard to know for sure.
If teachers are aligned with the values of the community, parents might not complain about what students are learning, Branch says. If parents do complain—because, say, they believe that the teacher has improperly brought up religion in the classroom—the principal might force the teacher to change his or her ways. If the principal backs up the teacher, it might become fodder for a lawsuit.
The courts have so far been on the side of the secular. Creationism has lost every major U.S. federal court case in the past 40 years, Berkman and Plutzer write. And not even the best-known opponents of evolution overtly come out against it. Take the Discovery Institute, which describes itself as an “educational and research organization” with “more than 40 affiliated scientists and scholars, many of whom think key features of life and the universe reflect evidence of intelligent design rather than an unguided process.” Its vice president, John West, told me via email that the best approach to teaching human evolution in public high schools is to “give students an accurate understanding of the current science, which includes exploring unresolved issues and areas where scientists continue to disagree.” These include, he said, “debates about how humans’ unique capacities for language, math, ethics, fire-making, and art developed in the history of life.” Sarah Chaffee, the institute’s program officer for education and public policy, told me, “The Next Generation Science Standards inform most states’ science standards. These standards mention many aspects of evolution, but they do not specifically reference human evolution.” If teachers aren’t teaching human evolution, she said, “it is very likely the main reason is solely the fact that it is not in the science standards.” (Branch says while it’s true that human evolution is not in the NGSS, other factors also might explain why teachers don’t present it.)
How does this variation in evolution education affect students? Plutzer suggested that “teaching the controversy” opens the door to the idea that matters of science are up to students to decide for themselves. “The broader consequence is that students will come away with the idea that important elements of science are based in values and not evidence, and that gives them license to reject other kinds of science,” he said.