With the exception of Ashley Tisdale’s new schnoz, everything is bigger in High School Musical 3: Senior Year, the first in Disney’s billion-dollar cable franchise to premier all bold and sparkly in your local cineplex. Set pieces spin and explode like Busby Berkeley on Red Bull. A lush orchestral score gives silly gravitas to teen swoon. And life-after-prom plot lines pile up like reckless bumper cars.

Tizzied preteens will make HSM3 a blockbuster by the end of the weekend, and why not: Without the burden of a tight Disney Channel budget, this one uses its big-screen allowance wisely, with eye-swirly art direction and a fortified script that doesn’t talk down to fans…yet still dots its “i”s with cartoon hearts. Enough of the umpteen pop songs, the fuel that drives these simple cinematic confections, properly stick in your head like a Milk Dud on a molar. HSM3 is a lot of goofy fun, maybe even the best in the series.

But FAIR WARNING, Mom and Dad: “Bigger” also applies to the aging actors, all of whom are now closer to home-pregnancy kits than home ec. Vanessa Hudgens, as virginal Gabriella, has sprouted boom-boom gams to rival Chita Rivera’s. Zac Efron, as Gabby’s beau Troy, flexes muscle-roped arms, newfound guns that director-choreographer Kenny Ortega curiously coats with gladiator-approved sweat.

And without giving away too much ('cause lemme tell you, THIS will be all the buzz), America’s sweethearts share a third-act moment usually framed by steamed-up windows in the backseat of a sedan. Yes, this is still the Mouse House, and the G-rating stands firm. But the subtext is obvious to all of us Gray Hairs: The East High gang has more on their mind than college aps.

For all the guss and glitz, HSM3 is basically built on the same synthetic premise as before (and before that). With graduation looming, hoops star Troy can’t decide between dribbling at a local college in Albuquerque or shooting for a spot at Juilliard. Either way, he'll be far from Gabs, who's off to Stanford. Best bud Chad (the exceptionally mop-topped Corbin Bleu) wants his buddy to stay close to home and stay focused on three-pointers. The rest of the gang -- dancing girl Martha, class prez Taylor, music savant Kelsi -- are all perfectly happy to flash high-beam smiles in the background.

And then, at last, there’s Tisdale’s Sharpay, the spoiled rich girl who just wants to be fabulously famous. Go ahead and rip on her rhinoplasty, but the blond bomber steals every scene like a pink-miniskirted thief. Tisdale can’t sing, and she really can’t dance, but her big, strutty number I Want It All is a triumph anyway, a dizzying send-up of Madonna and Marilyn and Mae West that finishes like a kid version of Jennifer Hudson’s Dreamgirls turn. Seeing as how Efron and Hudgens have all the acting chops of a twin pack of Ding Dongs, Ortega would have been wise to use Tisdale more.

The movie’s 112-minute run time is 20 minutes too long, and a couple of Troy and Gabriella’s mopier duets are the perfect chance to take your kids to the loo. In fact, the lovers-in-training actually fare better apart. With Walk Away, Hudgens gets to uncork a modern-day Hopelessly Devoted to You. His Scream is an over-the-top post-boy-band burner partly performed in a spinning, thunder-lit hallway; you'll laugh, your daughters will sigh. And Troy and Chad's bromantic gamboling in The Boys Are Back, set in a salvage yard, is like a cross between Footloose, The Road Warrior and La Cage aux Folles.

It all leads up to prom, then the spring musical, then graduation, each one fortified with robust song and dance. Ortega takes a few minutes in the movie's closing moments to linger lovingly on the face of each of his stars. They don’t pose as characters this time but as themselves, as if many of them know deep down that this will be as good as it gets. It’s a sweet tribute to a likable cast. But more than that, it’s a thank you and goodbye to the millions of boys and girls who have bought High School Musical CDs and DVDs and clothes and toys –- and who have grown up right before our eyes, too.