How and why does Graff isolate Ender from the rest of the boys?

In Chapter 4, the two anonymous voices plan to isolate Ender, because they think it will make him a good, creative leader. Moreover, he cannot be too nice or else the buggers would "have us all," but he will need to be able to work well with his subordinates. Ender is only six years old, but they will completely isolate him from the other boys in terms of friendly social contact, which means essentially that the adults will make all the other children hate him. This plan will develop Ender's character in the ways they want, but it may hurt him in terms of the usual gentlemanly social virtues. The adults acknowledge that they are going to break Ender down completely, in order to force him to put himself back together. He thus will be better than if they, less intelligent than he, had tried to do it themselves. Thus, they realize that they are trying to make someone who is better than they are themselves.

The author plays with the idea of human manipulation throughout the novel: when the ends involve saving the human race, are there any means that are off limits? In this case, Ender at least is intelligent enough to understand that he is being manipulated and can choose whether or not to keep participating in his own breaking down and building up. Therefore, while we might feel horrible for Ender in some ways, we can accept Ender's wise acquiescence in choosing to be unhappy for the sake of a greater good. In general, this is the problem that a good leader has; a truly good leader would rather be enjoying his own life, but he sacrifices his individual pleasure for the sake of the community.

Indeed, Ender is essentially separating himself from the others by means of his own character. He can be manipulated by the adults because he is the kind of person who already is so much like the one they want. Ender does not laugh at the other boys' jokes, nor does he come up with his own to share. He seems to consider himself superior to them, as it seems that he always has done. When he considers his imaginary television interview, he thinks, "They think I'm smiling at their joke, but I'm smiling at something much funnier."