Trivia

All the young actors who unsuccessfully auditioned for the role of Antoine were used in the classroom scenes.

So pleased with Jean-Pierre Léaud and his screen test (an informal conversation with the film's director being off-camera), François Truffaut doctored it into the finished film by using fade-outs and substituting his voice with off-camera female psychiatrist's voice.

Jean-Pierre Léaud's answers to the questions given to him by the psychologist at the camp near the end of the film were not scripted. François Truffaut told Leaud in advance about the scene for what to expect to a certain extent, and did provide some minor coaching when Leaud answered the question in between takes as to what was working and what was not, but at large, Leaud's answers are unscripted and ad libbed, per Truffaut's wishes, who wanted the scene to feel spontaneous and believable.

The English title of the movie "400 Blows" is a gross misinterpretation of the original title. The original title stems from the French expression "Faire les quatre cents coups", a figure of speech meaning "to live a wild life", as the main character does. Literal translation of the expression would be "to do the 400 dirty tricks".

The title of the film comes from the French idiom "faire les quatre cents coups", meaning "to raise hell".

François Truffaut: is seen riding next to Antoine in the centrifuge ride at the fair, and can then be seen smoking a cigarette just outside the ride.