Here's a great interview with Comic Book Resources:

Newcomer Joel Courtney is central to the story as young Joe Lamb, a teen dealing with the sudden loss of his mother and the far-reaching implications of that incident. His performance — really, that of all the child actors — is top-notch. It’s an especially impressive feat when you consider Courtney’s virtually non-existent acting background prior to his Super 8 experience.

“I’ve been acting for a year and a half. I’d had six acting classes before [shooting Super 8],” he told Spinoff Online last week. “It’s my brother, Caleb Courtney, who has wanted to act for a really long time.”

“I came down to visit him in LA, and that’s when I got the call about the [Super 8] audition. And so I was really excited. I wanted to get an audition for a commercial and [earn] $100, that was my goal for the summer. And I got Super 8, so …” Courtney trailed off, chuckling somewhat nervously at what is surely the latest bizarre turn in the roller-coaster he’s been riding for more than a year now.

It all started with a call from his acting coach, who’s also a casting director, with word of the Super 8 audition. Courtney went in and apparently left whoever watched him very impressed, as he received two immediate callbacks on that day alone.

“They had me sit in this other room, so I was kind of nervous, I didn’t know what they meant,” he explained. “They brought me some more scenes and I just figured that’s gotta be good. And then they did that again to me the same day, so that was kind of crazy. And then a while later they had me come back.”

“I came back 11 times, and a lot of them were chemistry auditions to see who would be really good friends,” he added. “Because in the movie, if you notice the chemistry between the kids, it looks like we’ve known each other since we were like really young because the chemistry there is just perfect between the kids. J.J. really wanted that to be spot-on, so a lot of them were inside acting with your friends and the other half was hanging out with all the other actors to see who the chemistry would be the best with.”

Interestingly, all of the scenes the kids worked on together turned out to be fakes. Courtney later realized that his audition scenes — some of them, at least — ended up in the movie in a modified form. But getting the groups together, sitting the kids down and forcing them to interact, was all about establishing a sense of how strong the chemistry would be.

The veteran actor among the group is Elle Fanning, younger sister of Dakota, who herself starred in Spielberg’s War of the Worlds. Courtney spoke glowingly of his co-star, and of the experience he picked up working alongside a fellow young performer with more than a decade’s worth of experience.

“It’s a lot of fun to play across from her, because she’s so kind and she’s so sweet, but then again she really is a good actress,” Courtney said. The chemistry across the entire group is what makes the movie work, though, what keeps the story together even when multiple plotlines are feeling underdeveloped and threatening to spin out of control. Super 8 never reaches that point, and that’s thanks in large part to how natural the kids are in their roles, much like the gang of Goonies Spielberg conceived back in the ’80s.

“Any time all of us kids are on set together, there is so much energy in that room it is insane,” Courtney said. “I don’t know how the crew put up with us and how J.J. stuck with us, but he did. It was a lot of fun. J.J. really wanted [us] to be overlapping. Not ‘you say your line, and then you say your line, and then you say yours.’ That doesn’t happen. People talk over each other naturally. That’s what he wanted.”