A Gallup poll late last year showed that only 28 percent of Americans accept the theory of evolution, while 48 percent adhere to creationism - the belief that an intelligent being is responsible for the creation of the earth and its inhabitants.
But if reluctance to accept evolution is not new, the ways in which students are resisting its teachings are changing.
"The argument was always in the past the monkey-ancestor deal," says Mr. Williamson, who teaches at Olathe East High School. "Today there are many more arguments that kids bring to class, a whole fleet of arguments, and they're all drawn out of the efforts by different groups, like the intelligent design [proponents]."
It creates an uncomfortable atmosphere in the classroom, Williamson says - one that he doesn't like. "I don't want to ever be in a confrontational mode with those kids ... I find it disheartening as a teacher."
Williamson and his Kansas colleagues aren't alone. An informal survey released in April from the National Science Teachers Association found that 31 percent of the 1,050 respondents said they feel pressure to include "creationism, intelligent design, or other nonscientific alternatives to evolution in their science classroom."
These findings confirm the experience of Gerry Wheeler, the group's executive director, who says that about half the teachers he talks to tell him they feel ideological pressure when they teach evolution.
And according to the survey, while 20 percent of the teachers say the pressure comes from parents, 22 percent say it comes primarily from students.
In this climate, science teachers say they must find new methods to defuse what has become a politically and emotionally charged atmosphere in the classroom. But in some cases doing so also means learning to handle well-organized efforts to raise doubts about Darwin's theory.
Darwin's detractors say their goal is more science, not less, in evolution discussions.
The Seattle-based Discovery Institute distributes a DVD, "Icons of Evolution," that encourages viewers to doubt Darwinian theory.