Marlon Brando originally signed for the role of Joseph Dobbs (Robert Preston), but quit the production before principal photography commenced. According to Bob Thomas's "Brando: Portrait of the Artist as a Rebel", Brando quit the production when he realized that James Mason had the better role, and that his flagging career would soon be revitalized by the The Godfather (1972). Preston, a fine actor, received poor reviews for his performance from Pauline Kael, among others. Brando subsequently was sued by producer David Merrick.
Sidney Lumet realized, after watching the daily rushes, that the terrific effect that the story had on stage - which it is inspired from - had totally disappeared on screen. He did not know where it came from exactly, and above all did not know how to fix it. He kept this awful feeling to himself because he did not want the other members of the crew, people he worked with, to lose their confidence in the film. He eventually never found what was wrong with the feature, compared to the stage play.
The film used students from Iona Preparatory School in New Rochelle, N.Y. as extras.
The original Broadway production of "Child's Play" by Robert Marasco opened at the Royale Theater in New York on February 17, 1970, ran for 342 performances and was nominated for the 1970 Tony Award for the Best Play. Robbie Reed was in both the original stage version and in this filmed production, but portrayed a different character in the film.
When author Robert Marasco originally wrote the play in 1966, he entitled it "The Dark." Harold Prince dropped his option before it was taken up by David Merrick.