I can hear the screams — high-pitched, sustained, the kind that pierce right through the eardrums and go straight to the brain — from outside the gymnasium of Kiser Middle School, and the kid’s not even inside the building yet.

But here he is now: Diggy Simmons, the teenage hip-hop phenom, son of the Rev. Run, nephew to kingmaker Russell, introduced to the world in the reality show “Run’s House” and now a star in his own right, after breaking with a mixtape in 2009, The First Flight, which he made available for free on the internet, and then quickly hitting the stratosphere.

Of course, I have no idea who he is. Not too many old farts like me do.

He hops from a black Mercedes touring van and heads directly for the TV cameras.

There he stands, confident and poised, his thumbs hooked into the pockets of his black skinny jeans, the black satin flight jacket hanging just right on his lean, 16-year-old frame, his magnificent high-tops laced just so, a kerchief flowing from out his back pocket.

He wears an easy smile amid the media swarm — local TV cams rolling, the morning crew from 102 Jamz milling in the periphery, a gigantic personal aide named Cortez who looks as if he could push the big Mercedes over on its side — and answers questions politely as the screams still seep from the gymnasium. And then, entourage in tow, he glides in a side door and up the stairs.

In the gym, a sample of Kiser students sit on the floor in a neat grid that threatens to descend into chaos as the screams bounce around the hardwood.

When the curtain opens, the wail crescendos and then falls off. It’s not Diggy himself but the 102 Jamz morning crew up there right now, B-Daht, Santillian and the lovely Tosha Makia celebrating their score, teasing it out.

“Who out there loves Diggy Simmons?”

Posters of the man-child line the front of the stage, a life-size cardboard cutout stands near the back curtain, which billows from the force of the screams.

Then the kid saunters onstage as casually as if he’s walking onto fifth-period gym. And the screams become so loud they take on mass.

He’s been making appearances all across the country this week: radio, television, theaters, the internet. He’s got a new CD to plug, Unexpected Arrival, dropping this week. But the surprise appearances like this one, in schools across the country to talk about peer pressure, bullying and the importance of education, are a deviation from the hip-hop publicity playbook. You’d never see Wiz Khalifa doing this. But the kid is so polite, so smart, so polished that he’s making it seem like the most natural thing in the world.

“A lot of this was his idea,” says Kathi Moore of Atlantic Records, Diggy’s label, who is traveling with him. “He’s young, you know? He’s 16. He enjoys it.”

Onstage the kid stays on message.

“Everything you do now can lead to a better life,” he tells the kids. “If you’re not focused, it won’t be as good…. It’s just about being yourself and not giving in to peer pressure. It’s just about everything you’re doing right now.”

I remember assemblies like this from my teenage years: The Positive Message. The Cautionary Tale. Your Permanent Record. Only when I was a kid it was usually some fat loser standing there in front of the whole school, nobody we respected or wanted to emulate. And my friends and I would generally already be high.

This appearance goes much better than those did.

After the kids ask questions — Do you play sports? What’s your favorite color? What’s your favorite subject in school? — Diggy’s biggest fan at Kiser, a tweener named India, rushes onstage and stands there transfixed. After he lays a hug on her she holds her hands to her mouth, breathless.

“Oh my God!” she says. More screams.

Moore allows me to move through the school with Diggy’s crew, behind the mountainous Cortez. We pop in on Miss Navarro’s language arts class — fitting, because English is Diggy’s favorite subject.

“I use words from my vocabulary lessons in my raps,” he tells the class. “If I didn’t know how to put my words together, how would I be able to be up here and talk to you guys in an educated way?”

Miss Navarro clearly approves.

One of the students asks him if he’s ever been bullied.

“Never,” he says, though he was in a regular school until 8th grade. “But I’ve seen people be bullied.”

I can’t help but glance over at Cortez, who looks like he’s built from bowling balls and truck tires, and feel sorry for anyone who tries to shove this kid into the girls’ bathroom.