To play youth thug Mick o'Brien, actor Sean Penn wanted to have his perfect teeth filed down and capped with ugly tops and have "maybe a few cracked ones" but Penn's mother, a dentist's daughter, intervened, ruling that "ruining perfectly good teeth is definitely going too far!".
To prepare for the movie, Rick Rosenthal and Sean Penn went out riding with the Chicago Police Dept. Gang Squad Unit. On the second night, Penn was mistaken for a real criminal and was assaulted by one of the officers.
During the scene where Sean Penn's character first enters the reform school and walks down the line in between the prisoners, Penn encouraged the actors to spit in his face and throw things at him. On the other hand, Esai Morales insisted that the actors who played the prisoners brush their teeth and use mouthwash before they spit in his face during his character's similar scene.
To prepare for his lead role as Mick O'Brien, actor Sean Penn let his hair grow long, had a tattoo inked on his arm, dressed in street gang garb, went on night patrol with the Chicago Police Gang Crimes Unit and almost got himself arrested at one point whilst doing all this.
Sean Penn once said of this film around the time of its first release: "This movie is a lot about drive, about frustrated drive and we all experience that. The kids in this movie feel they have very few choices - and they're unaware of those additional options they may have. I read the script and felt it was real. I went out into the areas of Chicago where we were going to shoot and there was stuff right out of our script, and even rougher. In a funny way I think people who see this film will be relieved to see that the rest of the world isn't like that. I want to see more films about the way the world 'really' is. With those so-called 'escapist' or 'pure entertainment' movies, you come out and the world seems so dull you want to go back inside. But I think reality should be more fun than fantasy. I think the real world's the most exciting of all, and that whatever is wrong with it can be fixed. I'm an opportunist".
The passage written on the board in the classroom is from Jack London's 'Call of the Wild'. Presumably, this is also the novel O'Brien and Horowitz read and discuss while sitting in their room during a later scene.
One of only four feature films featuring actor Eric Gurry who played Sean Penn's little cell-mate side-kick Horowitz. This was Gurry's second feature film after just being introduced to audiences the year before playing one of Al Pacino's children in Author! Author! (1982).
Sean Penn insisted on being called the name of his character, Mick O'Brien, during production of the movie. Moreover, when Penn spent a week's filming at the St. Charles maximum-security youth reformatory, his official name-tag identification read "Mick O'Brien".
The movie that the boys are seen watching is "Kiss of Death", 1947. The scene shown is where Richard Widmark shoves Mildred Dunnock down a stairs in her wheelchair. At the time this scene was considered very shocking.
The name of the youth jail was the "Rainford Juvenile Correctional Facility". Established in 1919, its motto was "Justice with Mercy". The name of the other prison facility, the gaol for adults, was the "Illinois State Penitentiary".
When Esai Morales' character is leaving home to go to the drug deal, he tells his mother "La bendicion" (Blessings), to which his mother replies, "Que Dios te bendiga" (May God bless you), this is a traditional Hispanic cultural greeting and farewell that one gives to elder family members. It's also said as "Bendicion (insert elder family member's title), to which the same response is given. Although it's very very common among Hispanics of all countries, it is very rarely ever portrayed in movies or television programs with Hispanic characters.
Jamie Lee Curtis and Clancy Brown are both in the movie. Clancy Brown has a large part and Jamie Lee Curtis has a very small cameo. Clancy Brown and Jamie Lee Curtis would also star in Blue Steel, seven years later in 1990.
Horwitz gets even with everyone who has hurt or humiliated him. He fire bombed the alley where he was beaten up. He caused Wagner to get his finger snapped in a mouse trap after Wagner beat him up. He got even with Viking twice. First, when Viking insulted Horwitz and Horwitz dumped the tray of food on him. The second was when he wired the boom box to explode after Viking tripped him.