You might get pushed around. In fact, you will get pushed around. And when you do, don't come crying to me. Got it? This is Battle School, not nursery school."
"What are we supposed to do, then?" asked a boy, a really small black kid who had a top bunk near Ender's.
It cannot be Shafts, because as he was already mentioned by name prior to this quote.
I'm thinking that it might be Alai, based on the passage found in the original 1985 edition:
They grinned. Then Ender said, "Better invite Bernard."
Alai cocked an eyebrow. "Oh?"
"That little slanty-eyed butt-wiggler?"
Ender decided that Alai was joking. "Hey, we can't all be niggers."
Alai grinned. "My grandpa would've killed you for that."
"My great great grandpa would have sold him first,"
"Let's go get Bernard and Shen and freeze these bugger-lovers."
The main objection I have to this is the following passage:
Ender smiled, "Missed you at practice, Alai."
"I was there. But they had your army in a separate place. Looks like you're big time now, can't play with the little boys anymore."
"You're a full cubit taller than I am."