The movie is based on Nick McDonnell’s 2002 novel of the same title about a Manhattan teen who deals drugs at his private school. (Mr. McDonnell, son of Sports Illustrated editor Terry McDonnell, attended Riverdale prep and wrote the book when he was just 17.)

The film, set for release in 2010, has enlisted some of Manhattan’s less experienced young actors, including 23-year-old Chace Crawford, who is set to play the lead role of "White Mike"; the 20-year-old Zoe Kravitz, daughter of Lenny; Ralph Lauren model Cody Horn and—and!—Liam McMullan, son of party photographer Patrick, for whom this is a first movie role.

“Joel specifically wanted kids that would be believable high school kids,” said Jessica Kelly, the casting director for the film. “It was important from day one of casting to treat this like a documentary—over-privileged, under-loved teens in New York exist and, in order to care about these characters, they had to be 100 percent human and believable.”

Was Ms. Kelly nervous about casting Mr. Crawford, best known for his work on TV's Gossip Girl but otherwise lacking much big screen exposure, for the lead role?

“No,” she replied. “Chace definitely has star quality and is also a really good actor. I am excited for him to show what he can do with this character.”

Mr. McMullan had originally tried out for Mr. Crawford’s role.

“He wasn't right but he was too unique and colorful and ‘of this world’ to not bring him back for Joel,” said the casting director. “Joel thought of the character Royal for him right away.”

Reached by phone last week (Mr. Schumacher objected to having the Daily Transom visit the set), Mr. McMullan was sitting in his trailer—yes, he’s got his own—in a Thom Browne suit with a tutu sewn inside. He was waiting to shoot the next scene with Ms. Kravitz at a house party inside a brownstone.

“My character is friends with all the girls in the movie,” said Mr. McMullan. “He’s like the gay fashionista guy.”

The model Ms. Horn, also the daughter of Warner Brothers chief operating officer Alan Horn, was taking a break from the shoot, having just arrived in the Hamptons, when the Daily Transom caught up with her this week.

“I got the part through this photographer I work with,” she said, "Bruce Webber?" (Yeah, we might know that guy.)

One day, according to Mr. McMullan, the cast was shooting on the Upper East Side when a troop of tween girls gathered on the sidewalk to look on. Mr. McMullan asked if they might be waiting for a sighting of Mr. Crawford.

“They were like nooo!’” Mr. McMullan recalled,  “And I was like, 'Well, do you want him to come meet you?' And they were like 'Yeaaah!' So I called him up and all these girls jumped me and stole Chace Crawford’s number out of my phone!”

He added, "Joel is always joking that we’re going to win for the most attractive cast."