Irony as They Are Cast: In the film, neither of the Aguilar brothers can speak any English. According to an interview in a Sports Illustrated "Where Are They Now" issue, Jaime Escobedo (Jose) and George Gonzales (Miguel) were in fact fluent in English and didn't know how to speak Spanish. They had to learn how to speak their entire dialogue strictly in Spanish before filming began.
The studio originally wanted Burt Lancaster to play Buttermaker. The screenwriter (Bill Lancaster, Burt's son) vetoed that idea as he didn't want people to think he was playing off his father's fame.
Steve McQueen and Warren Beatty were offered the role of Buttermaker, but both turned it down due to involvements with other film projects.
Jodie Foster was originally cast as Amanda, but she dropped out in order to play Iris in Taxi Driver. Sarah Jessica Parker tried out for the role. Kristy McNichol was offered the role of Amanda, and even successfully auditioned for the part. According to McNichol, the producers told her afterwards when they would begin filming and that she had to start preparing, but over one weekend they changed their minds, and she was disappointed to hear that they gave the role to Tatum O'Neal. She and O'Neal would co-star in the 1980 film Little Darlings.
In the second film, given how they ended the character arc of Timmy Lupus, one can only imagine how big a role he could've played if Quinn Smith were available to participate more in the film.