A climax is the culmination of action—the most intense, exciting, or important part. It usually comes near the end of the book or chapter.
 Let's take a look at some of the things that happen in "November." In this chapter, Holling begins reading The Tempest after school. He attempts to make up for spoiling the class cream puffs by buying some with his own money, and he impresses Mr. Goldman, the baker, with his Shakespeare recitation so much that he lands a role in the Long Island Shakespeare Company's holiday performance.
Despite Holling's efforts to replace the spoiled cream puffs, he fails again when the class rats get into them. Mrs. Baker ends up buying more cream puffs and telling the class that Holling brought them. This shows Holling that she actually may like him, after all.
None of these actions qualifies as the climax because while they develop characters, plotlines, and relationships that will continue throughout the rest of the book, none of them acts as the culmination of action.
But in the last two pages, something truly significant happens—the culmination of a storyline that shows the teachers at Holling's school worrying about their husbands, who are fighting in Vietnam. Holling is present when Mrs. Bigio tells Mrs. Baker that her husband was killed.
This event is clearly the climax of the chapter, because it's the most important and significant event. It leads Holling to understand that while The Tempest has a happy ending, in real life happy endings aren't guaranteed.

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