"We put it in three times on the Monday, three times on the Tuesday, three times on the Wednesday, left it out on Thursday, then put it in right at the end of the Friday show. Some of the kids toward the end of the day Wednesday were saying, not Wanda the Witch again. When Wanda the Witch came back Friday, they jumped and clapped. Kids reach a saturation point. But then nostalgia sets in."

Not long afterward (and quite by accident), the Sesame Street writers figured out why kids like repetition so much. The segment in question this time featured the actor James Earl Jones reciting the alphabet. As originally taped, Jones took long pauses between letters, because the idea was to insert other elements between the letters. But Jones, as you can imagine, cut such a compelling figure that the Sesame Street producers left the film as it was and played it over and over again for years: the letter A or B, etc., would appear on the screen, there would be a long pause, and then Jones would boom out the name and the letter would disappear. "What we noticed was that the first time through, kids would shout out the name of the letter after Jones did," Sam Gibbon says. "After a couple of repetitions, they would respond to the appearance of the letter before he did, in the long pause. Then, with enough repetitions, they would anticipate the letter before it appeared. They were sequencing themselves through the piece; first they learned the name of the letter, then they learned to associate the name of the letter with its appearance, then they learned the sequence of letters." An adult considers constant repetition boring, because it requires reliving the same experience over and again. But to preschoolers repetition isn't boring, because each time they watch something they are experiencing it in a completely different way. At CTW, the idea of learning through repetition was called the James Earl Jones effect.

Blue's Clues is essentially a show built around the James Earl Jones effect. Instead of running new episodes one alter another, and then repeating them as reruns later in the seasons — like every other television show — Nickelodeon runs the same Blue's Clues episode for five straight days, Monday through Friday, before going on to the next one. As you can imagine, this wasn't an idea that came easily to Nickelodeon. Santomero and Anderson had to convince them. (It also helped that Nickelodeon didn't have the money to produce a full season of Blue'sClues shows.) "I had the pilot in my house, and at the time my daughter was three and a half and she kept watching it over and over again," Anderson says. "I kept track. She watched it fourteen times without any lagging of enthusiasm." When the pilot was taken out into the field for testing, the same thing happened. They showed it five days in a row to a large group of preschoolers, and attention and comprehension actually increased over the course of the week — with the exception of the oldest children, the five-year-olds, whose attention fell off at the very end. Like the kids watching James Earl Jones, the children responded to the show in a different way with each repeat viewing, becoming more animated and answering more of Steve's questions earlier and earlier. "If you think about the world of a preschooler, they are surrounded by stuff they don't understand — things that are novel. So the driving force for a preschooler is not a search for novelty, like it is with older kids, it's a search for understanding and predictability," says Anderson. "For younger kids, repetition is really valuable. They demand it, When they see a show over and over again, they not only are understanding it better, which is a form of power, but just by predicting what is going to happen, I think they feel a real sense of affirmation and self-worth. And Blue's Clues doubles that feeling, because they also feel like they are participating in something. They feel like they are helping Steve."

Of course, kids don't always like repetition. Whatever they are watching has to be complex enough to allow, upon repeated exposure, for deeper and deeper levels of comprehension. At the same time, it can't be so complex that the first time around it baffles the children and turns them off. In order to strike this balance, Blue's Clues engages in much of the same kind of research as SesameStreet — but at a far more intense level. Where SesameStreet tests a given show only once — and after it's completed — Blue's Clues tests shows three times before they go on the air. And while Sesame Street will typically only test a third of its episodes. Blue's Clues tests them all.

I accompanied the Blue's Clues research team on one of their weekly excursions to talk to preschoolers. They were led by Alice Wilder, director of research for the show, a lively dark-haired woman who had just finished her doctorate in education at Columbia University. With her were two others, both women in their early twenties — Alison Oilman and Allison Sherman. On the morning that I joined them they were testing a proposed script at a preschool in Greenwich Village.

The script being tested was about animal behavior. It was, essentially, a first draft, laid out in a picture book that roughly corresponded to the way the actual episode would unfold, scene by scene, on television. The Blue'sClues tester played the part of Steve, and walked the kids through the script, making a careful note of all the questions they answered correctly and those that seemed to baffle them. At one point, for example, Sherman sat down with a towheaded five-year-old named Walker and a four-and-a-half-year-old named Anna in a purple-and-white checked skirt. She began reading from the script. Blue had a favorite animal. Would they help us find out what it was? The kids were watching her closely. She began going through some of the subsidiary puzzles, one by one. She showed them a picture of an anteater.

"What does an anteater eat?" she asked.

Walker said, "Ants."

Sherman turned the page to a picture of an elephant. She pointed at its trunk.

"What's that?"

Walker peered in. "A trunk."

She pointed at the tusks. "Do you know what the white things are?"

Walker looked again. "Nostrils."

She showed them a picture of a bear, then came the first Blue's clue, a little splotch of white and black tattooed with one of Blue's paw prints.

"That's black and white," Anna said.

Sherman looked at the two of them. "What animal could Blue want to learn about?" She paused. Anna and Walker looked puzzled. Finally Walker broke the silence: "We had better go to the next clue."

The second round of puzzles was a little harder. There was a picture of a bird. The kids were asked what the bird was doing — the answer was singing — and then why it was doing that. They talked about beavers and worms and then came to the second Blue's clue — an iceberg. Anna and Walker were still stumped. On they went to the third round, a long discussion of fish. Sherman showed them a picture of a little fish lying camouflaged at the bottom of the sea, eying a big fish.

"Why is the fish hiding?" Sherman asked.

WALKER: "Because of the giant fish."

ANNA: "Because he will eat him."

They came to the third Blue's clue. It was a cardboard cutout of one of Blue's paw prints. Sherman took the paw print and moved it toward Walker and Anna, wiggling it as she did.

"What's this doing?" she asked.

Walker screwed up his face in concentration. "It's walking like a human," he said.

"Is it wriggling like a human?" Sherman asked.

"It's waddling," Anna said.

Sherman went over the clues in order: black and white, ice, waddling.

There was a pause. Suddenly Walker's face lit up. "It's a penguin!" He was shouting with the joy of discovery. "A penguin's black and white. It lives on the ice and it waddles!"