Teachers who are unable or unwilling to teach the theory of evolution in biology might be one reason U.S. students are falling behind in science, according to new research.

The study, done at Penn State University, polled 926 high school biology teachers from around the country. It found that a large majority are reluctant to address the evolution in their classrooms.

The findings come at a time when the national Center for Education Statistics, a part of the U.S. Department of Education, released findings that said only 21 percent of students in grade 12 scored at or above proficient in 2009, with 60 percent reaching the level of basic. President Barack Obama called in his state of the union address for more teachers of math and science, and noted that other countries that have emphasized education those fields have produced more competitive students.

The National research Council recommends that teachers introduce to students the evidence that evolution actually occurred, and use it as a unifying theme in different areas of biology. But Berkman and his co-author, Eric Plutzer, found that only 28 percent of teachers do this at all. A small minority - 13 percent - explicitly present creationism or intelligent design in a positive light.

But the crux of the study is what the authors call the cautious 60 percent who neither advocate for the science of evolution nor push creationism, but simply avoid the issue altogether. Teachers may want to avoid controversy, but the problem, Berkman says, is that it undermines science as a mode of thought and means of finding out about the world. Many high school students in the U.S. take no science classes at all, and for 25 percent of high schoolers, biology is the only one.

Not having biology taught properly, Berkman says, makes it harder for students to understand science later on. A sound science education is important, he adds, given that science and technology are so important in everyday life.

The theory of evolution states that life forms will change over time in response to their environment, and the fraction of individuals in a species with one or more inherited traits will differ. The cause is natural variation within species, which affects how well they survive in a given environment -- or not. Sometimes species will split into two or more different ones, and sometimes they will die out.

The simplest way to solve this problem is to change the ways people who will become teachers are taught the subject before they ever get into a classroom, Berkman says. A class covering evolution as a subject by itself makes the future teacher comfortable with the material. Even science majors, he says, sometimes don't take such a class, and not every biology teacher majored in science.

Some teachers try to present both sides, he notes, but the problem with that is that it puts science in the same class of knowledge as an opinion, as though well-established principles could be debated.

The data Berkman and Plutzer gathered didn't show trends over time. But Berkman says one bright spot is that standards are being imposed in more school systems. Since many of these standards include evolution, younger teachers are more likely to hew to them. In addition, the high-profile battles over standards have had some effect. They have started to get scientists more involved, Berkman said.