To understand what Sylvia means when she says, "But ain't nobody gonna beat me at nuthin" at the end of "The Lesson," it is important to understand what has happened before this declaration. The narrator is an African American girl whose family struggles economically. She hangs out with her cousin Sugar and a larger group of friends and schoolmates. A new arrival in the neighborhood, a woman named Miss Moore, takes it on herself to educate the children by leading them on excursions and trying to teach them lessons.
The story tells of an excursion they all take to a toy store in a white neighborhood in which all of the toys have unbelievably high prices. Miss Moore is hoping that the children will learn sociological lessons about the differences between rich and poor people and the unfairness of elite privilege. Sugar gets the idea when she says, "This is not much of a democracy if you ask me. Equal chance to pursue happiness means an equal crack at the dough, don't it?"
However, Sylvia does not see the excursion experience in this way. When they all reach the toy store, she hesitates before going in. For some reason she can't identify, she feels shame. She is not at first sure why. She thinks, "I have never ever been shy about doing nothing or going nowhere." Miss Moore is trying to teach her a lesson, but instead she takes it personally. She doesn't like that she feels shame, even if only temporarily. At the beginning of the story she displays a proud, even a haughty, self-image. She refers to the days when "everyone was old and stupid or young and foolish and me and Sugar were the only ones just right."
The last line of the story—"But ain't nobody gonna beat me at nuthin"—says several things. First of all, it is a rejection of the shame that Sylvia felt just before she entered the toy store. It is also a rejection of the simplistic message about society that Miss Moore had been attempting to teach. At the same time, Sylvia's worldview has been shaken. She wants to "think this day through" because she is determined, in spite of the revelations of the day, to come out on top again, even if she has to revise the way that she sees and reacts to the reality around her.