5. Dustin was cast almost immediately from a pool of over 1000 kids
Basically, the idea here is that Gaten is one of the coolest and sweetest kids around. It’s like when Room came out and everyone was obsessed with Jacob Tremblay for a hot minute.
In Gaten’s case, he left an impression immediately. He was the first kid actor among the Stranger Things group to be cast. And according to the Duffer Brothers and the casting crew, it all boiled down to “authenticity.”
"“We looked at 1,000 kids. Most kids, you can turn off their auditions after five seconds, because there’s nothing authentic about it. The minute we saw Gaten [Matarazzo], who plays Dustin, we basically cast him off the first tape that he sent in. When you see someone like Gaten, and he pops the way he does, you’re just like, “This kid, we’re putting him in the show, 100 percent.” — Matt Duffer"
Additionally, it seems like Gaten Matarazzo snagged the role before he even met the Duffer Brothers in person. He impressed them so much — two guys who don’t really have a ton of prior experience with children, or the casting thereof — he earned his place as the lovable dork of the group. And I bet he really poured his heart into it before he even understood how big the project would turn out to be.