LIBERTY, Mo. — Monday morning, Room 207: First day of a unit on the origins of life. Veteran biology teacher Al Frisby switches on the overhead projector and braces himself.
As his students rummage for their notebooks, Frisby introduces his central theme: Every creature on Earth has been shaped by random mutation and natural selection -- in a word, by evolution.
The challenges begin at once.
"Isn't it true that mutations only make an animal weaker?" sophomore Chris Willett demands. " 'Cause I was watching one time on CNN and they mutated monkeys to see if they could get one to become human and they couldn't."
Frisby tries to explain that evolution takes millions of years, but Willett isn't listening. "I feel a tail growing!" he calls to his friends, drawing laughter.
Unruffled, Frisby puts up a transparency tracing the evolution of the whale, from its ancient origins as a hoofed land animal through two lumbering transitional species and finally into the sea. He's about to start on the fossil evidence when sophomore Jeff Paul interrupts: "How are you 100% sure that those bones belong to those animals? It could just be some deformed raccoon."
From the back of the room, sophomore Melissa Brooks chimes in: "Those are real bones that someone actually found? You're not just making this up?"
"No, I am not just making it up," Frisby says.
At least half the students in this class of 14 don't believe him, though, and they're not about to let him off easy.
Two decades of political and legal maneuvering on evolution has spilled over into public schools, and biology teachers are struggling to respond. Loyal to the accounts they've learned in church, students are taking it upon themselves to wedge creationism into the classroom, sometimes with snide comments but also with sophisticated questions -- and a fervent faith.
As sophomore Daniel Read put it: "I'm going to say as much about God as I can in school, even if the teachers can't."
Such challenges have become so disruptive that some teachers dread the annual unit on evolution -- or skip it altogether.
In response, the American Assn. for the Advancement of Science is distributing a 24-page guide to teaching the scientific principles behind evolution, starting in kindergarten. The group also has issued talking points for teachers flustered by demands to present "both sides."
The annual science teachers convention next week in Anaheim will cover similar ground, with workshops such as "Teaching Evolution in a Climate of Controversy."
"We're not going to roll over and take this," said Alan I. Leshner, the executive publisher of the journal Science. "These teachers are facing phenomenal pressure. They need help."
About half of all Americans dismiss as preposterous the scientific consensus that life on Earth evolved from a common ancestor over millions of years. Some hold to a literal reading of Genesis: God created the universe about 6,000 years ago. Others accept an ancient cosmos but take the variety, complexity and beauty of Earth's creatures as proof that life was crafted by an intelligent designer.
Religious accounts of life's origins have generally been kept out of the science classroom, sometimes by court order. But polls show a majority of Americans are unhappy with the evolution-only approach.
Daniel Read, for instance, considers it his Christian duty to expose his classmates to the truths he finds in the Bible, starting with the six days of creation. It's his way, he said, of counterbalancing the textbook, which devotes three chapters to evolution but just one paragraph to creationism. A soft-spoken teen with shaggy hair and baggy pants, Daniel prepares carefully for his mission in this well-educated, affluent and conservative suburb of 28,000, just outside Kansas City, Mo. He studies DVDs distributed by Answers in Genesis, a "creation evangelism" ministry devoted to training children to question evolution.
Other students gather ammunition from sermons at church, or from the dozens of websites that criticize evolution as a God-denying sham. They interrupt lectures to expound on the inaccuracies of carbon dating; to disparage transitional fossils as frauds; to show photos of ancient footprints that they think prove humans and dinosaurs walked side by side.
Most will learn what they need to pass the test, but some make their skepticism clear by putting their heads down on their desks or even stalking out of class.
Liberty High School senior Sarah Hopkins was proud of her response when a botany teacher brought up evolution last year: "I asked, 'Have you ever read the Bible? Have you ever gone to church?' "
Such personal questions can make teachers uncomfortable, but they're fairly easy to deflect. Far tougher are the science-based queries that force teachers to defend a theory they may not ever have studied in depth.