First, Graff wants Ender isolated from the kids so he doesn’t pick up their thought processes (which, yes, is a little strange, since these kids are supposed to be the super geniuses of the world – not bad folks to copy). Second, he also wants Ender isolated from the adults so Ender doesn’t rely on them. This comes up a bunch of times in the novel. For instance, Graff later says that Ender can’t have anyone who he looks up to as parents (5.16) and that Ender can’t expect help out during the war itself (5.5).

Graff will pretty soon reverse himself on this statement and tell Anderson that he is Ender’s friend (4.98). But as far as Ender knows, this is it – Graff isn’t his bud and, frankly, none of the kids are either. (Especially after Ender broke that one kid’s arm.) But here’s one thing that we know that Ender doesn’t, which is that Graff really is his friend. So, while Ender thinks he’s all alone in the world, we know that he secretly has support.

Ender later says pretty much the same thing to Bean, but here Ender is hearing it from Graff. Ender might have thought that Battle School was a chance to start over and become friends with kids who are as smart as he is. But Graff has other plans: he wants to isolate Ender, and here he says the only way out of that is for Ender to be the best. OK, so being the best isn’t necessarily the best way to make friends, but that’s another issue that Ender will face. (Though it’s interesting that the issue of skill and social position are so connected.)