Young Sheldon” is a prequel to the most popular comedy on television — “The Big Bang Theory” — but it’s a very different show.

Not just because it’s set in 1989, when Sheldon Cooper was a 9-year-old genius entering high school. Not just because it’s about Sheldon and his family.

It’s a very different format. “Big Bang” is a multicamera sitcom, filmed in a studio in front of an audience. “Young Sheldon” is filmed on location and shot like a movie.

There’s a very simple reason for that. The show centers on a 9-year-old actor (Iain Armitage) and features his twin sister and teenage brother. “It seemed like the more appropriate way for them to do the best work was in a closed setting,” said executive producer Chuck Lorre.

CBS is airing the “Young Sheldon” pilot on Monday, Sept. 25, at 7:30 p.m. on CBS/Ch. 2; it returns with its second episode in its regular time slot on Thursday, Nov. 2, at 7:30 p.m.

The new series is very much like “The Wonder Years”; it’s about a young boy and his family, and the adult version of the boy serves as the series narrator. “Young Sheldon” wis narrated by older Sheldon (Jim Parsons, who has played the character on “Big Bang” for a decade).

The writers/producers looked to “Wonder Years” for inspiration because “nobody did it better,” said Lorre. He is TV’s most successful sitcom producer; his credits include “Roseanne,” “Dharma & Greg,” “Two and a Half Men,” “Mike & Molly,” “Mom” and, of course, “The Big Bang Theory.” But this is his first filmed comedy and the first with narration.

It’s a wholly different way to tell a story, and the working process is very different,” Lorre said. “It’s much slower. But the end result is something to be proud of, really. I love the pilot.”

It’s a very good pilot. Armitage (“Big Little Lies”) does a great job capturing Sheldon as a 9-year-old — you can see how he became the Sheldon “BBT” fans love. And Armitage has some of what Lorre called the “magical quality” that Parsons brings to the adult Sheldon, who “can be despicable.”

He can be so difficult and hard on his best friends, and yet, somehow, he has a quality as a person where the audience forgives him,” Lorre said.

Not that young Sheldon is exactly like older Sheldon.

When you take those same qualities and ask a 9-year-old to bring that, it’s a brat. That’s not something that’s very pleasant,” Lorre said.

Young Sheldon is “much more vulnerable and naive” than older Sheldon, Lorre said. “More innocent and hopeful,” said creator/executive producer Steven Molaro.

But “Young Sheldon” is not just about Sheldon, it’s about his mother (Zoe Perry), father (Lance Barber), sister (Raegan Revord) and brother (Montana Jordan), too.

(And you’re not imagining things. Perry looks and sounds a lot like Laurie Metcalf, who plays Sheldon’s mom on “Big Bang Theory” — because she is Metcalf’s daughter.)

Part of the fun of writing the series was not just to watch how Sheldon develops, but to see how his family has to adapt,” Lorre said.

I think anytime that you have a kid that isn’t exactly typical,” Molaro said, “it can be difficult for the child, and it can be difficult for their siblings and for the parents.”

Lorre and Molaro (who’s also an executive producer of “Big Bang”) are still adjusting to writing and producing a filmed comedy. Molaro said he “marveled” when they shot the first family dinner scene in the “Young Sheldon” pilot.

In the time it took us to shoot that, we could have shot two episodes of ‘Big Bang Theory’ in front of an audience,” he said. “Like, wow. Just one scene.”