“You should’ve told me. You should always confide in your teachers.” (Situational Irony)
When Sourpuss the teacher wants to hear an excuse for why Antoine was absent the previous day, Antoine tells his teacher that his mother died. Sourpuss is shocked to hear it and suddenly becomes sympathetic. Uncharacteristically, he says, “You should’ve told me. You should always confide in your teachers.” This line strikes an ironic tone, because until now, Sourpuss has hardly seemed like an understanding confidant. Quite the contrary, he is a mean and harsh teacher, who favors punishment over understanding. Because the viewer sees the world from Antoine's perspective, and recognizes that the adults around him are unkind and do not seek to understand how children feel, this line of Sourpuss's strikes us as especially ironic, and even disingenuous.
Antoine's Lie (Dramatic Irony)
Making Antoine's report that his mother has died all the more ironic is the fact that he is lying. Needing a good excuse for not being in school the previous day, Antoine lies and says it is because his mother has died. He knows that this lie will not get him in trouble with Sourpuss, and will likely get him pity rather than punishment. The viewer knows that he is baldly lying to his teacher, but his teacher has no idea, thus creating an instance of dramatic irony.
René's Father Finding René Smoking His Cigars (Dramatic Irony)
Another instance in which we the viewer know more than the characters is when René's father comes into the room where René and Antoine were just smoking and playing a game. Antoine hides on the side of the bed, but the smoke still lingers. While René's father doesn't know that Antoine is staying at the house, we can see Antoine in the foreground of the bed, creating dramatic irony.
Antoine Plagiarizes (Situational Irony)
When Antoine returns home after having run away, his mother tries a different parenting tactic, and exhibits some love and affection towards him for the first time. While this is partly because she fears that he will reveal her affair to Mr. Doinel, it is also because she wants to find a way to reach through Antoine's misbehavior and motivate him. She offers him 1,000 francs if he writes a paper that is in the top 5 in his class. He happily accepts. For the next week, we see him intently reading Balzac, even building the author a shrine. It seems as though Mrs. Doinel's bargain worked, that she motivated Antoine into caring about literature and into using his clearly dynamic but untapped mind in the classroom. Thus, it comes as an ironic twist when Sourpuss reveals that Antoine completely plagiarized his essay directly from Balzac. It seems that Antoine was so inspired by Balzac that he used the writer's words as his own. It is ironic that while Truffaut really makes it seem that Antoine has learned how to love reading and composition, he is still cutting corners and making poor choices after all.