LOS ANGELES -- Jamie Lynn Spears is looking for the show business equivalent of lightning striking twice, if not exactly in the same place.

"I'll probably do a lot of acting first, then go to singing," says the precocious kid sister of pop star Britney Spears.

"But I am going to definitely sing someday," she adds after a brief moment of reflection. "So when I do start singing, buy my album."

For now, the youngest of three Spears siblings (the oldest is a brother, Bryan), says she has her hands full balancing school and her responsibilities as the youngest cast member of the comedy-variety show "All That" (8 p.m. Saturdays on Nickelodeon).

A sort of "Saturday Night Live" for kids, "All That" is in its eighth season on Nickelodeon; Jamie Lynn joins a veteran cast of actors who are an average of 4 years older than her.

It was a slightly awkward adjustment for the stick-thin 11-year-old from Kentwood, La., who looks like a younger, skinnier version of her 20-year-old superstar sister.

But having wrapped a season of new episodes that began airing in September, all concerned say Jamie Lynn fit right into what she acknowledges was her first substantial acting job. Earlier this year, she made a brief appearance as a younger version of her sister in "Crossroads," Spears' film debut, and she's done a handful of commercials.

"At first I was too scared to act in front of these people, so I was real shy," says Jamie Lynn, gesturing toward castmates Shane Lyons and Chelsea Brummet as the three unwind on a couch backstage.

"But then," she adds, "they were actually really nice. I thought they were going to be these serious people. But they were a lot of fun."

It didn't hurt, the others say, that Jamie Lynn was willing to jump right into scenes that included dousing her with egg yolk and tossing her into trash bins. Soon she was engaging in the cast's seemingly endless stream of offstage banter.

"I was expecting someone who was going to be a little kiddish, kind of immature," says Lyons, 15. "But what we got was someone who could relate and talk and just mess around with us on our level."

"Jamie has the maturity level of, like, a 15-year-old, which is awesome," Brummet adds.

High praise indeed, which Jamie Lynn acknowledges with a shy nod of her head; it's one of the few times the diminutive chatterbox is quiet. Usually she's full of stories, particularly about school and her home in Louisiana.

"You know how everybody says thingy-mah-jig?" she asks. "I could swear I made that up. Everybody says it, from Kentwood to California to New York, and I'm telling you, I made it up. I said it one day, and the next day the whole school was saying it."

She'd like to be as big a star as her sister, she says, but she really doesn't think of Spears as a famous person.

"She's just her," Jamie Lynn says, adding that her sister gave her tips on making it in show business after she'd auditioned and won a spot on "All That."

"She did, yeah, I'm sure she did," she says, trying to recall the advice. "But I don't know what she said now."