In Chapter 10, Charlie taunts Headmaster Nolan with a knowing moment of verbal irony, to raucous cheers from his peers:
"Yes, he is, just a moment. Mr. Nolan, it’s for you,” Charlie said with mock seriousness. The dean’s face turned beet-red. “What?” Nolan screeched. Charlie held the receiver out to Nolan. “It’s God. He said we should have girls at Welton[.]"
The students are gathered in the chapel for a meeting addressing the “unauthorized and profane” article Charlie illicitly published advocating for girls at Welton. While Charlie is obviously not on the phone with God, his sarcastic disruption of the meeting clearly communicates his disrespect for Welton's rules and regulations while amusingly protesting Welton's policy against admitting women. The unheralded disturbance of the student-wide meeting with a sarcastic quip directed at the head of school, who has just threatened expulsion, evokes much laughter from his fellow students. The fact that this instance of verbal irony occurs in the very meeting intended to address Charlie's similarly mocking article heightens its significance: Charlie is being as brash and rebellious as possible.
Religion and God are evoked frequently throughout the story, most relatedly when Mr. Keating says “gods were created, gentlemen,” as he describes the Dead Poets Society. Recall also that Headmaster Nolan is compared to a vicar in Chapter One, following a school-wide meeting in this very chapel. Mocking God while inside a chapel is a serious matter indeed, especially for a vaguely religious institution like Welton. Charlie's verbal irony is thus a major step in the ever-growing rebellious attitudes of the Dead Poets Society. The students are beginning to outwardly revolt against Welton, as opposed to merely breaking the rules in secret.
The last scene of the novel involves a moment of situational irony as Headmaster Nolan teaches English after firing Mr. Keating, who has entered the classroom to gather his things:
The irony of Nolan’s choosing the Pritchard essay just as he walked in the room was just too incredible.
Headmaster Nolan chooses to begin his class the same way Mr. Keating began his second class in Chapter 5: with an essay by Pritchard detailing how to evaluate poems. Mr. Keating, however, made the class rip the essay out of their textbooks, believing the essay to be valued only by the "academic hoi polloi." Kleinbaum rightfully acknowledges the irony of the situation—though he doesn't realize it, Mr. Nolan is embodying the “academic hoi polloi” whom Mr. Keating believes to entirely miss the point of poetry. Mr. Keating’s emphasis on passion and individuality is at odds with Headmaster Nolan’s focus on success and conformity. Mr. Keating’s earlier command to rip out the essay—which appeared at the time to be a theatrical means of conveying the idea that poetry is about passion—was in fact a necessary prophylactic against the academic hoi polloi, whether or not he knew it at the time.
The irony of the situation also amusingly highlights the growth of the students. They no longer fit in at Welton, and without the Pritchard essay they are literally unable to be educated in the boring and conformist way Nolan, the story’s antagonist, would like them to be. Immediately following this moment of irony, Todd inspires the rest of the students to stand up on their desks in tribute to Mr. Keating, reenacting their earlier class in which Mr. Keating urged the students to stand on their desks to view the world from a different perspective. With Mr. Keating gathering his things and Nolan serving as interim teacher, the students endorse Mr. Keating's pedagogical approach by standing on their desks, shouting “O Captain! My Captain!”, and refraining from reading the essay that they have removed from their textbooks.