MAD PROPS: Dan Schneider delights in the candy-colored sets and toys like Sterling motorcycles on Sam & Cat, the latest star-making vehicle in his 20-year string of tween hits.

"Hey, guys! Look what I got for my butt!" Ariana Grande is cooing in a breathy Marilyn Monroe voice, standing on the Sam & Cat living-room couch, shaking her skinny ass in supertight jeans. Grande, who plays ditzy Cat, is wearing a furry robotic tail embossed with the words tush tail—a contraption purchased with ill-gotten magic-ATM money. It's the day after the surprise visit from the network overlord, and Schneider, who thinks the rump-shaking needs to be more vigorous, steps away from his monitor to show her how it should be done. "Ari, try it like this," he says. Schneider hops up on the couch and bounces his own, ample ass vigorously, arms flapping at his sides.

At least when executed by Grande, the Tush Tail conceit feels vaguely dirty—that a girl would wear a heart monitor attached to her chest and, depending on whether she's happy or sad, the tail either stands on end and wags or falls flaccid. Intentional or not, this kind of innuendo is new in Schneider's world; until now, the most graphic Schneider has gotten was when Sam and Freddie swapped spit on iCarly, and Sam and Cat discuss sex as much as Ernie and Bert. "I've been staying away from the boyfriendy, girlfriendy stuff as of late," Schneider tells me—since tween boys are turned off by romance. But message boards are being lit up by boys who find Grande majorly feel-up-able, and it's hard to imagine her butt talk isn't intended to titillate, especially given Grande's breathy, porn-suggesting line reading. Guys discovered by Schneider have certainly fared well—notably Nick Cannon and SNL castmates Thompson and Tarran Killam. But Schneider is the unrivaled master at finding young girls whom other young girls would die to be besties with and whom boys, as they approach full teenhood, realize they're in love with. Amanda Bynes, Jamie Lynn Spears, and Miranda Cosgrove were all once that girl.

And now it's the 20-year-old Grande, Sam & Cat's breakout sensation. Last year brought a hit album that debuted at No. 1, drew comparisons to Mariah Carey, got Grande on The Tonight Show and Late Night With Jimmy Fallon, and led to a standing ovation from Lady Gaga at the American Music Awards. While Jennette McCurdy, the show's Sam, proves a willing trouper, Grande cannot be torn away from hair and makeup for five minutes to say nice things about the man who made her a star. Instead, her mother, Joan, dressed head-to-toe in black and wielding a garish crystal-covered marker, appears. I ask whether everything is okay with her daughter, since today she's introducing Schneider and the crew to her new boyfriend, Nathan Sykes, of the English/Irish boy band the Wanted (who've since broken up), but just a couple weeks previous, she was warring on Twitter with her ex, the YouTube comedian Jai Brooks of the Janoskians, who accused her of relationship overlap. (@arianagrande: "You said to me if I didn't come back to you, you'd make me look bad to the entire world . . . I'm no longer afraid of you or your lies anymore.") The elder Grande's eyes narrow. "Oh, that's been cleaned up, by the boy himself, who couldn't clean up his trails of lies," Joan says darkly. "Nasty kid."

"We were a big Nickelodeon household," says Joan, who is from Boca Raton and has been "divorced multiple, multiple times." "When Ariana was 4½, she said, 'I want to be on Dan's show, All That.' So I said call Nickelodeon and ask. She called 411, got Nickelodeon's number in Orlando, and said, 'I want to be on All That.' The woman said, 'Get an agent, honey,' and hung up."

It took a decade, but she did just that. Grande played a cheerleader in a 2008 Broadway musical called 13. The show lasted only a couple of months, but it was long enough to attract the attention of Schneider, who was looking to cast a singer in a small role on Victorious.

Now, according to her mother, she can't walk down the street in North America or Europe without being mobbed. It's been tough. "She's never been the type to enjoy the red carpet or photo shoots," Joan says. "She doesn't think of herself as that special. She doesn't want to be on the cover of magazines. She wants to sing all over the world and make people laugh." Apparently, magazine covers are tough to avoid. A couple of weeks later, in Complex, Grande describes her repeated encounters with demons; then, in Cosmopolitan, she opens up about her relationship with Sykes, a romance that reportedly imploded before the issue hit newsstands. That same month, she took to Twitter to deny Star's report that she was dating Entourage's Adrian Grenier.

Early-onset fame can create monsters. There's no telling whether Grande's demons will follow her, but up to this point, Schneider's been lucky. "I've never had a kid who really, really spun out of control," he says. "At the very worst, I've gotten a little bad attitude, showing up a little late, clearly only slept two hours. I've had to sit kids down and say, 'Come on, we've gotta take the job a little more seriously.'" Zoey 101 wrapped months before 16-year-old Jamie Lynn Spears announced she was pregnant, and Amanda Bynes' mental-health crisis began years after The Amanda Show signed off. Bynes, he says, "never had a problem, was easily one of the most talented kids I've ever worked with." Maybe it was purely good timing, or maybe he was a particularly good manager of young actors. He was, after all, once one himself.

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Schneider is, by most people's definition, a fat guy, but considering how much weight he's lost in the past year, it seems heartless to say so. At his peak, he tipped the scales at well over 300 pounds. After a decade of marriage, Schneider decided to follow the low-fat philosophy of his wife's business. "I'm down 102 pounds," he says. "I've thrown away three levels of fat clothes: super-fat clothes, ridiculously fat clothes, and the very fat clothes. I'm on a mission to get under 200 pounds for the first time in my adult life."

As much as Schneider has hated being overweight, he'd likely not be in entertainment if not for those extra pounds. He grew up in Memphis, the son of a prominent Jewish lawyer. He was funny and popular but a terrible student. Despite his lousy grades, he wanted to go to Dartmouth, partly because he'd heard that it was the model for Animal House's Faber College. But in high school, at a talent show at a community center, he trotted out impressions of Star Trek characters, Elvis, Gilda Radner's Roseanne Roseannadanna. "I got huge laughs," he says. "It was like a drug for me."

After graduation, he started taking acting classes. One day, his acting teacher told him that a Judd Nelson movie was shooting at a local college campus and there would be auditions for speaking roles, one of which was a chubby junior. Schneider more than nailed it. "The role was supposed to be four days—it turned into four weeks," he says. "They kept writing me more lines."

There is Schneider, all of 19, on the DVD cover of that film, Making the Grade, in a blazer and rep tie, shoving a sandwich into his face. Similar sandwich-centric parts in eighties fare followed; in Better Off Dead he played Ricky, the corpulent mama's-boy ogre who spends the movie cock-blocking John Cusack. Roles turned out to be surprisingly easy to get, but the typecasting took a toll. "There was a point where I said to my agent, 'Please don't send me up for auditions where I'm the overweight guy shoving a hamburger in my face.'"

Schneider found deliverance in playing Dennis Blunden on the ABC sitcom Head of the Class, which ran from 1986 to 1991. "Dennis was funny and cool," he says. On set, Schneider bonded with Brian Robbins, who played the show's biker-jacket-wearing streetwise kid, Eric Mardian. Robbins, who would go on to attain super-producer status for creating shows like Smallville and One Tree Hill, was already trying to write his way off the acting treadmill. During a hiatus from shooting, Robbins and Schneider holed up in their Toluca Lake apartment complex and tapped out a script for Head of the Class. "We turned the script in and it was shot a few weeks later," Robbins says.