"I NEED A THREE-LETTER WORD for station," Dane said on my first morning in Rock Island. He'd just come back from a training session on the Caney Fork and was sitting cross-legged and shirtless in the living room, working on a lesson in his eighth-grade textbook, The Growing Vocabulary: Fun and Adventure with Words. The exercise felt more game show than homeschool, and Dane was relying heavily on audience participation.

"Man, this is hard," said Dane. "How about ‘to cook slowly, five letters.'"

"I think you mean six letters," suggested Nick, who lives with the Jacksons and occasionally tutors Dane. "Try simmer."

"Simmer is a word?"

Dane's 13, but at four foot six and 71 pounds, he looks more like ten. Like his dad, he's ripped, only on an even tinier scale, with apricot-size biceps, toothpick calves, and actual pecs. He was three when the family moved into the RV, and, along with Emily, he's been home-taught his whole life.

A buoyant little pinball propelled not by ego but by pure, guileless joy, Dane ran his first Class IV rapid a month before his third birthday; when he tipped over, E.J. rolled him up by hand. Emily—who is a carbon copy of Kristine, with thick, chocolate-brown hair and a swimmer's build—inherited her father's competitive spirit. "Emily sizes up the other paddlers and does everything she can to make sure she's better than them," says E.J. "Dane's less externally motivated. He just loves to kayak." Which is to say, the Jackson kids take after their dad in their own ways, two halves to E.J.'s paradoxical whole: On the water, E.J. is fluid but controlled, more a technician than an artist.

He trains relentlessly—several hours twice a day on the Caney Fork—and last winter on the White Nile he and the rest of the Jackson team staged mock world championships, judging each other's moves and crowning victors. While younger paddlers (Dane included) experiment with risky combo maneuvers—like a McNasty that morphs into a sideways-flipping roundhouse—that can cause them to wash or "flush" off the back of the wave, E.J. sticks to his dependable arsenal of high-scoring moves and muscles through them with the precision of a figure skater. "His tricks aren't fancier or flashier than his competitors'," says Clay Wright. "He just throws down more of them." E.J. doesn't disagree: "Most of my successes come from being last man standing."

Despite his own obsessive focus, E.J. insists he didn't push his kids into kayaking. "We've never given any indication that we expect them to kayak," he says. "In fact, I thought that if they did, it would be that much less kayaking for me." The kids started paddling seriously in 2003—Dane was eight and Emily was 12, and E.J. was their coach—and not long after began racking up impressive showings on the junior playboating circuit. Dane finished first among junior men at the U.S. team's 2006 time trials on the Ottawa; Emily won the 2005 and 2006 women's open division at the Teva Mountain Games, in Vail.

Of course, in a house full of competitors, someone's bound to have a bad day now and then, but Kristine refuses to tolerate any moping. "You're allowed to cry for five minutes," she says. "My job is make sure that—win, lose, or disgrace yourself—you still come back to the same situation in this family. No matter what happens, we're still us, and we're still great. If you have anything to complain about, you're barking up the wrong tree."

Neither Emily nor Dane plans on going to college, and their parents aren't pushing that either. "I don't see any real value in it," E.J. says. "Of course, if they want to go, we'll be behind them 100 percent, but right now I'd say both of them have the equivalent of a Ph.D. in kayaking."