Like when the eager puppy, a guide dog in training, runs down a hallway and begins sliding on the shiny tile floor.
"A body in motion stays in motion," Mark Rosenblum, a science teacher at Everett's Sequoia High School, said with a chuckle, paraphrasing one of Isaac Newton's laws of motion. "Or that every action has an equal and opposite reaction."
And a genetics lesson can be much more fun with a 62 pound, tail-wagging dog sitting just feet away, as Rosenblum explains how two black Labrador retrievers can have black, chocolate or yellow offspring, depending on the genetics of their parents.
Rosenblum's guide dog is but one example of how pets and live animals are used in classrooms in school districts throughout the county.
Many parents may remember their own school days, when reptiles, hamsters, rabbits and chicks were as much a part of the typical classroom setting as pictures of U.S. presidents.
In recent years, though, school districts have begun adopting policies that in many cases limit or even ban animals in the classroom unless they're part of science projects.
Animals may be cute and fun to be around. But they can spread disease and cause allergic reactions in students. And students are exposed to animal wastes.
With these and potential liability concerns, the state is asking school districts to draw up policies on what animals, other than service animals, should be allowed in schools.
The requirement, scheduled to go into effect in July, is now on hold due to the state's budget problems.
"It's simply an ongoing issue schools have had to deal with," said Donn Moyer, a spokesman for the state Department of Health. "The idea behind it is to protect the health of students."
The number of children with asthma increase as they get older, from 15 percent of sixth-graders to 21 percent in seniors, according to a 2008 state Department of Health report.
"You have to be very cautious about the environment in which they learn," Moyer said.
Students can be infected with bacteria, such as E. coli, MRSA or salmonella, after touching pets and not washing their hands, said Nickol Finch, who heads the exotic and wildlife services at Washington State University.
Students can get ringworm from guinea pigs, she said. And turtles, snakes and lizards can spread salmonella.
Germs can be passed when a child shares lunch with an animal, allowing it to take a bite of a carrot, for example, and then the child eats the rest of the vegetable.
Influenza, including H1N1, can be passed from humans to ferrets, or from ferrets to humans, she said.
Finch said she also has another concern, unrelated to germs.
"I'm a veterinarian," she said. "I look at it from the animals' perspective. I've seen what kids have done to animals."
That includes the guinea pig that was dropped and brought in for treatment for a broken leg or gerbils that were squeezed too hard.
"It happens," she said.
Some school districts already have guidelines in place. The Edmonds School District's policy, which took effect in November, is one of the most recent.
Many animals are banned, including dogs, cats, chickens, ducks, reptiles, snakes -- even ant farms.
Turtles bigger than four inches, fish and frogs are allowed if they are kept in clean aquariums.
Animals on the banned list can get the OK if they are being used as part of student instruction.
Therapy and service dogs, such as Ernie, a one-year-old Labradoodle at College Place Elementary School, are allowed.
The new policy "has helped us determine the purpose of animals to see whether they are instructional or only a pet," said Justin Irish, principal at College Place.
The school's fourth-grade teachers are now discussing whether they want to apply for a waiver to have chicks in their classrooms. For at least five years, they incubated eggs in the classroom so children could learn about the chicken's life cycle, Irish said.
Now they aren't sure if they want to do it.
"We are in talks to see the instructional value," Irish said. "We are asking: Are the kids learning something?"
The Everett School District's policy, adopted in 2001, bans a number of animals: chicks, raccoons, squirrels, reptiles and centipedes.
Dogs and cats are allowed if they've been vaccinated, don't have fleas, ticks or mites and if they wear a collar or are leashed on school grounds.
Mukilteo schools put the kibosh on having pets in the classroom about three years ago, unless the animals are part of a science class.
"The proliferation of animals was starting to become an issue," spokesman Andy Muntz said.
Among the issues district officials considered was who would take care of classroom pets during holiday and summer breaks, he said. There also was concern that some students may have pet allergies or simply not tolerate pets.
"It's easier not to deal with it," he said.
Although there was "a little furor" when the policy first began, "now, no one is complaining anymore," Muntz said. "As soon as you start making exceptions, it's 'how about this?' Then you're back to where you started."
For at least 10 years, the Monroe School District has required that all classroom animals be used as part of an education plan, spokeswoman Rosemary O'Neil said.
Students from kindergarten to eighth grade have a "no touch" policy with the animals. High school students can work with animals in supervised programs like Animal Science or the FFA club, O'Neil said.
Currently, animals are used in science classes in the Snohomish School District, said spokeswoman Kristin Foley.
Chicks, turtles and fish are examples of animals brought to classes as exhibits. Dead animals, like frogs, are used for dissecting.
Animal cages are labeled, requiring students and staff to wash their hands before and after handling animals, and there are written instructions of what to do in case of a bite.
Yet even with policies like these and warnings about the potential for spread of disease, the National Science Teachers Association endorses having animals in the classroom as part of a science class.
Pets can excite students about science and can be a valuable learning tool, Francis Eberle, the group's executive director said.
"The experience of caring for live animals is an experience that can't be simulated and is a valuable tool to engage students in hands-on learning and inquiry," he said.
Guide dogs in training have been part of Rosenblum's Sequoia High School classrooms for 15 years. It's part of their basic training before they're sent off for more intensive training with California-based Guide Dogs for the Blind. Dogs are taken to another classroom if any student is allergic.
Brenden Nguyen, 17, said Franklin lifts spirits just by his presence.
"When you're feeling down, he always cheers you up," he said.
In addition to helping illustrate scientific principles, the dogs have helped bridge barriers, Rosenblum said.
In one case, a former student was dealing with the loss of a family member. "The boy was despondent," he said, but was comforted by being able to spend time with Morrison, the dog Rosenblum was then raising.
The dogs have also helped students open up who have previously have had problems with teachers. "Sometimes it's just enough to break the ice with a kid to talk to me.
"Kids sign up for my class initially because they want to be with the dog," Rosenblum said. "Then, I win them over with the science and math."
Sharon Salyer: 425-339-3486; firstname.lastname@example.org.
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