The climax in a drama is the decisive moment. In the play The Miracle Worker it occurs in Act Three when Helen realizes that the word is the thing and the thing is the word. When Helen realizes that the strange gestures Annie is making in her hand are the word for water and she remembers her baby word "wa-wa" as she is being forced to pump water, language is unlocked for her enabling her to learn.
From the e-notes plot summary: "In the yard, Annie is forcing Helen to pump water, meanwhile spelling w-a-t-e-r into Helen's hand, and "Now," as Gibson says, "the miracle happens." Helen has the breakthrough Annie has prayed for, and runs around the yard touching, and learning from Annie the names of the pump, the stoop, the trellis, and more."