The climax of Bradbury's short story is when the sun comes out for the first time in seven years. The kids have locked Margot in a closet and to their astonishment, the sun comes out. They bolt outside to the sun, frolicking and playing in the illumination. They play until it begins to rain and then they have to come back inside. It becomes evident to them, in a dawning- like realization, that they left Margot in the closet.
This moment of the sun appearing is the climax because it is the point in which the action is the greatest. In the conflict between Margot and the group of students, it is at this point where the tension between both is the highest in an almost contradictory moment of unity and symmetry. It is Bradbury's genius to construct the situation so that Margot was actually right. Rather than praise her for her correct world view, the kids flock towards her absolute sense of accuracy and her vision, something that she is not able to appreciate because of being marginalized. The height of the plot, the moment where the action is most intense, is in this moment of unity, one in which there is validation but not for the person who advocated it. In this, there is a climax and a sense of diminishing action appears at the end when the children come to the silent realization that they have to release Margot out of the closet.