Preddy bet the contractor the price of the job that he had goofed. The geometry teacher showed the contractor that two four-inch pipes still had less area than one six-inch pipe (a circle's area is calculated by multiplying pi by the radius squared). Preddy won the bet.
Preddy's contractor is not the only believer. This summer, Preddy was one of only 25 math and science teachers selected from the eastern United States to attend a NASA-sponsored science educators' workshop at the Goddard Space Flight Center in Greenbelt, Md. They were given the chance to design an experiment that would be launched on a space shuttle.
NASA picked Preddy's experiment, which will send bulbs into orbit to determine the effects of space travel on plant growth. It is scheduled to blast off in June.
Preddy is an energetic iconoclast who rides a motorcycle, favors cowboy hats and boots, and dons a hard hat in the classroom when he is about to lead students in solving a particularly thorny problem.
He tells students upfront that most teachers of math err by not explaining its applications in the world.
And he makes a bargain: If he cannot prove the utility of any given exercise, he will skip it.
"It's outrageous that someone would make you do something and not tell you how to use it," he said.
The former systems analyst for Scott Paper Co. was considering a career change in 1991 when he was laid off. It was a Monday, Preddy recalls. On Tuesday, he registered for education classes at Widener University.
"He brings a lot to the table," said Robert Murphey, Preddy's professor at Widener and now a colleague at Haverford High.
Murphey said Preddy tied his work experience to the classroom in a way that students responded to. "It's a resource and a gift," Murphey said.
The trick, Preddy said, is to teach students the tools and never just have them memorize the answers. "That'll cause them to think things through so much that they'll get it," he said.
At the end of the school day, Preddy waits in his classroom for students seeking more help after school. Jayme Hubbard, a 16-year-old sophomore, was stuck on a geometry exercise involving cubes of various sizes.
Preddy unceremoniously dropped a plastic bag full of wooden blocks onto Hubbard's desk and told her to start building cubes. As she did, recording numbers for the formulas she had to divine, he gently prodded her with questions. "Do you see any patterns?" he asked.
When she fell silent, puzzled, Preddy had Hubbard go back over what she had already accomplished.
She had worked out two formulas and was closing in on the last two when Preddy challenged her to take the blocks home and finish on her own.
"The physical example was great," Hubbard said. "He showed me what to do, and I took that and used it to find the answer."
At the NASA workshop, Preddy and other teachers met with top scientists who explained projects such as investigating global warming and tracking El Nino.
"I was humbled," Preddy said. And energized.
In his experiment, each teacher will get bulbs from the shuttle flight and bulbs that stay on Earth. Students will plant the bulbs and chart their growth.
"I am thrilled that it got picked," he said.
It is hard to tell which thrills Preddy more - his experiment or the prospect of having one more vehicle to attract students to the utility of math.
"They're not necessarily enjoying this," Preddy said of his methods. "But ultimately they do, because the experience is one that they know is valuable."
Mark Stroh's e-mail address is firstname.lastname@example.org