ON a hot June day, Jamie Lynn Spears' bangs kept falling in her face. The 14-year-old actress was shooting a scene for her Nickelodeon show "Zoey 101" at Pepperdine University in Malibu, where the series is filmed. In the complicated segment, she had to ride a scooter, take off her helmet and tie her co-star's shoelaces together. But her hair was causing continuity problems. "Why don't we just cut it off?" Ms. Spears asked helpfully, after the fifth time a stylist came to try to tame her bangs.

Is the modish and athletic Zoey, Ms. Spears - yes, she's Britney's younger sister - is one of Nickelodeon's most valuable commodities. On all of television, there is only one show more popular than "Zoey 101" with tweens - the get-them-while-they're-young demographic from 9 to 14 that many advertisers love. And that's a little show on Fox called "American Idol."

Over all, according to Nielsen Media Research, Nickelodeon is a dominant No. 1 among tweens, beating cable competition like the Disney Channel and Cartoon Network. That supremacy is due to Nickelodeon's TEENick block, which in addition to "Zoey 101," features scripted, live-action series like "Drake & Josh," "Ned's Declassified School Survival Guide," "Romeo!" and "Unfabulous." To capitalize on the shows' successes, Nickelodeon has announced that there will be a "Zoey 101" apparel line in the fall, as well as an "Unfabulous" soundtrack, which is scheduled to be released in late September. All the series have been shooting new episodes this summer for fall premieres.

As a rule, these shows use actual young people - as opposed to network series like "The O.C.," where teenage characters are usually played by actors in their 20's. As a result, they have a lifespan of three or four years before the cast gets too old. In order to grab young viewers' attention, the shows present fantasy worlds of school and home life, where tweens fill their leisure time with a multiracial group of friends, clothes and gadgets. Songs are another fundamental element, particularly if the star of the show is musically inclined. And increasingly, these series cast the relatives of very famous people.

"Zoey 101" features all of these prerequisites. The series made its debut in January and takes place at a fictional, elite boarding school that has admitted girls for the first time. Ms. Spears' character and her friends face the middle-school challenges typical for tween television: make your backpack look cooler, get out of gym, settle differences among pals. Ms. Spears sings the theme song, of which her sister was a co-writer.

During an interview on the set, Dan Schneider, the creator of "Zoey 101," said, "There's no brilliant combination to it." Mr. Schneider was himself a child actor - he was Dennis Blunden on the ABC sitcom "Head of the Class" from 1986 to 1991 - and currently has two other shows besides "Zoey 101" on Nickelodeon, "Drake & Josh" and "All That," a sketch comedy program.

To gauge the response of his viewers, Mr. Schneider said, he reads Internet message boards. "I think that they want to see kids that reflect what their friends are like," he said. "But they also want to see kids that are like the friends they wish they had. I can't tell you how much work we put into casting this show."

The show was built around Ms. Spears, who was already in the Nickelodeon stable, as Mr. Schneider cast her on "All That" when she was 11. He had first auditioned her after a Nickelodeon executive asked him if he would like to meet with Britney Spears' sister. "I said, 'Sure,' " Mr. Schneider recalled. "You know, I'm not stupid, I knew that would bring a lot of attention to 'All That,' and it would be a good thing. I was just hoping she'd be good."