While the climax of the novel could be seen as Winnie sacrificing herself for Mae in the prison, I would suggest another moment to serve as the climax of the novel. The climax of Tuck Everlasting is where Winnie's emotional construction of reality is fundamentally tested. Once Tuck gives her the bottle of water to make her immortal upon her turning seventeen, the choice that forms the climax of the novel becomes evident. Winnie's choice of rejecting immortality for human life is the climax of the novel. It is climactic because it involves Winnie having to choose to be immortal or to embrace living a life where change, growth, and death result.
This choice forms the climax of the novel in a couple of ways. The first is that it brings forth Winnie's condition of being positioned between equally desirable, but ultimately incompatible courses of action. On one hand, Winnie has come to understand that being human involves change and growth. Her experiences with the Tucks have revealed to her that human consciousness is formed as a part of life, "always growing and changing, and always moving on." At the same time, Winnie also must reconcile with the "tugging and insistent" bonds that have formed between she and the Tucks. She has also developed feelings for Jesse that are reciprocated. The choice that Winnie must face is to live with Jesse in immortality in which they can see the world and experience life with one another. The other side of this coin would be for her to simply live life and experience it with the vitality and limitations that it presents. A choice of this magnitude is intensely agonizing. The fact that it is not simple and fraught with profound implications on both sides is why it represents the climax of the novel.
One of the ideas to emerge out of Tuck Everlasting is that individuals must strive to live life to its fullest. The idea of not being afraid of death as much as "the unlived life" is an essential element to the narrative. It is for this reason that the climax of Winnie pouring the water from the eternal spring on the toad is so significant. Winnie recognizes the need for life, in particular hers, to always change. Part of this is in her own maturation in sacrificing for something else. The same tenets of self- sacrifice that saved the Tucks is what saves the toad when she says, "There! You're safe. Forever."
With this action, the climax presents itself because it Winnie has made a choice. She has chosen life. Winnie embodies what it means to be a human being, a condition filled with intensity, happiness, sadness, and perseverance. These qualities are what defines her sense of character and her legacy, a name that lives on even after she dies. In this light, her choice to choose life represents the climax because she has found a way to garner immortality as a result of her choice. When Angus remarks that "dying's part of the wheel," it makes Winnie's choice all the more climactic.