The fundamental assumption that undergirds the novel's plot is that the culture of the Sand Dunes tribe is in extreme danger of elimination. Instead of rounding them up and exterminating them (which also happens, unfortunately), typically what will happen is that the authorities will ship the children off to boarding schools where they will be systematically re-educated. In this novel, school is a tool for brainwashing children into becoming the type of person which is allowed in American culture.
Typically, America is a symbol for the great melting pot effect of democracy, but in this novel, American school is a tool used to reduce diversity, and the assumption is that if people don't fit a certain mold, they are not welcome to stay in America. The assumptions of this tribal culture are strikingly opposed to the dominant narrative that American schools use to define the nation. This is why the native people talk about American schools as brainwashing, propagandizing culture machines.
This point of view is not automatically granted by the plot. For instance, Indigo has to suffer the exact re-education that she has grown up to despise, but her education (although it did rewire her cultural assumptions) also brought her into the future, giving her new opportunities, allowing her a chance to become a full-blown citizen of the world. The truth seems to be more complex than either party suggests. The suggestion of the novel is that these dilemmas between culture are part of fate. Indigo never forgets, however, the antagonism and oppression that existed against her community.
