According to Dr. Seuss, the film's creator and co-writer, one of the 150 boys vomited on the piano while filming. This caused a chain reaction and they were left with 150 vomiting boys. Seuss said later that the film's reviews were similar to this incident.
Following a poor preview screening, the entire film was reworked, eschewing much of the social commentary and the various Dr. Seuss grotesqueries in favor of family-friendly sentimentality. Nine songs were cut, subplots were eliminated, new scenes were shot and existing scenes were rearranged.
The words Bart recites while making the blood oath with Mr. Zabladowski are taken word-for-word from the Scout Law of the Boy Scouts of America (trustworthy, loyal, helpful, friendly, etc.).
When Bart and Mr. Zadlabowski are taken to the dungeon via elevator, there is no reference to a third floor dungeon by the Elevator Operator. The third verse of the Elevator Operator's song was cut due to increasingly horrific lyrics referring to household appliances. The complete deleted verse went as follows: "Third floor dungeon, household appliances/Spiked beds, electric chairs/Gas chambers, roasting pots/And scalping devices." (the reference to "gas chambers" was probably regarded to be in bad taste since the film was made so soon after World War II and the Holocaust)