Writer and Director Dito Montiel was reluctant to cast Shia LaBeouf in the role of young Dito, because Montiel was intent on casting an unknown. After the first rejection, however, LaBeouf pushed for one more audition. He came into the casting office, punched a hole in the wall, and convinced Montiel that he could bring the requisite amount of anger to the role.

Shia LeBeouf and Channing Tatum only had one day to get to know each other, despite playing childhood friends. They decided to go out and get drunk on the streets of New York City. They remain good friends to this day.

The real Laurie died of A.I.D.S. before Dito Montiel returned to New York City. He decided to write her as being alive and well in the film, partially as a way of being able to see her again, saying, "I wanted to walk down those streets again and fall in love with Laurie again, it would have been nice to have had that moment at the end of the film where Dito met Laurie, reconnecting as adults."

When Dito (Shia LaBeouf) and Mike (Martin Compston) are talking about what music they should play, Mike says that they should sound like Black Flag or Major Conflict. Major Conflict is a New York hardcore band, in which Director Dito Montiel played when he was young.

Channing Tatum read the script while in the bath, and claims it made him burst into tears.

Robert Downey, Jr. had originally planned to direct the film himself. But in the four years of pre-production, he became busy with various other projects. Eventually Dito Montiel decided to direct, despite having only made a couple of short films beforehand. Robert Downey, Jr. remained on as a Producer.

Channing Tatum lost "a lot of weight" to play Antonio, at his own suggestion. Dito Montiel said that Tatum was a little too good looking to be Antonio, but ultimately brought the right amount of emotion for the character.

Many of the locations used in the film were the same places where the actual events had occurred. The conversation between Dito and Flori in the early morning for example is down the street from where the real Antonio had lived. Dito Montiel joked that many of his childhood friends would hang around the set for filming, and tell the cast members "I never would have said that."

Final film of George DiCenzo.

Dito Montiel's original vision had kids from the streets of New York City playing the characters, and he held seven open casting calls. He was eventually persuaded to allow professionals to audition, joking that he protested against every single actor who ended up cast. He later said that each cast member ended up being perfect in his or her role.

Eleonore Hendricks was originally cast as the young Laurie, who was a white girl in real-life. But Rosario Dawson expressed interest in playing the older Laurie. As Dawson is mixed race, and Hendricks is white, Melonie Diaz was chosen to play the teen-aged Laurie. Hendricks was then given a smaller role as Laurie's friend Jenny to make up for it.

Characters alternately refer to Dito with different pronunciations. This is true to real-life, as Dito Montiel claims his family were the ones who pronounced it "dee-to", but his friends said "ditto". This is reflected in the film, where Dito's parents use the former and his friends use the latter.

Martin Compston was cast as Mike based on his performance in Ken Loach's Sweet Sixteen (2002), for which he won Best Actor at the British Independent Film Awards. Executive Producer Trudie Styler was on the jury for said award.

Robert Downey, Jr. jokes that at one point, Trudie Styler locked him, Dito Montiel, and Alex Francis (who was head of development) into her apartment in New York City, and wouldn't let them out until they had "nailed the structure".

The real Monti appears in a scene after the end credits.

The real Antonio can be heard over the phone trying to persuade Dito to come home. If you listen closely to Dito in the conversation, it's not Robert Downey Jr speaking.

When casting the teenage Laurie, Dito Montiel was torn between Melonie Diaz and another actress who resembled Rosario Dawson more. Deciding that Melonie's performance was stronger, he cast her instead. After the film came out, he said many people told him that the two looked so alike. Although fifteen years separate the two time lines, there is only five years between the two actresses (although Melonie Diaz is playing a character at least ten years younger than she is).

The detail of Nerf still living with his mother - who is then said to be so ashamed of him she hides from him on the street - was added in after Dito Montiel met another old friend in that situation. The real Nerf was baffled by this and asked "what are you doing to me?" - as in real life he became an ambulance driver and is "doing great", according to Dito Montiel.

In the scene where Monty (Chazz Palminteri) has a seizure, Antonio (Channing Tatum) throws a table through the glass window of a door. This was improvised by Channing Tatum, who got so wrapped up in the scene, he nearly lost control. The rest of the cast stayed in character, and finished the scene, and Dito Montiel liked it so much, he kept it as the final version.

Giuseppe and Mike are shown dying. Their real life counterparts lived however, and the characters are a combination of them, and other people Dito Montiel knew in his childhood. The real Giuseppe became a career criminal, and was eventually deported to Italy. Mike moved to Essex, where he married and started a family.

Giuseppe's death scene was supposed to have him riding on top of the train and falling off. This scene is taken from a real-life incident, where a kid Dito Montiel used to know, rode around on the tops of trains. Due to insurance reasons, it was impossible to put Adam Scarimbolo on top of a train, and so it was changed to him being run over on the tracks.

The real Antonio actually managed to escape from prison briefly, before going back in. When Robert Downey, Jr. found this out, he wanted it put in the movie; he was convinced, however, to leave it out, as there was no way to incorporate it into the story.

The real Guiseppe was apparently very excited when he heard he'd be killed off in the film.