James is that kid who sits in the back of the class, but always has the right answers. He's a little boy genius, but he's got a bit of a bug about it, so he tries to fly under the radar. In fact, he even tries to dumb it down in the gifted class, because he's afraid the other kids will make fun of him for his big brain. That's how smart this kid is.
But as with most gifts, James's brain is a bit of a blessing and a curse. It's useful, because Dicey knows he can help Maybeth learn to read. But it also makes him stand out, as he points out to Dicey in this exchange about his classmates:
"I thought they were smart," Dicey insisted. "Like you."
He shook his head. "Not like me," he said. "I thought they might be, but they aren’t." (2.95-96)
Those two eldest Tillermans are a lot alike, aren't they? They both feel like oddballs (and let’s face it: they’ve got some pretty oddball life experiences under their belts). So it's no wonder that Dicey constantly worries about how James is fitting in at school.
Yet we're willing to bet that James will settle into his brain eventually. Because what matters here is family, and his family counts on his brain. Where would Maybeth be without her big brother to help her? James's teaching Maybeth shows that James can be Dicey's ally, rather than just another sibling to be taken care of. In realizing that James's smarts can be an asset, instead of a burden, Dicey sees that once again, the Tillermans can pretty much do anything. If a member of their family struggles, Dicey and James have the intelligence and creative thinking skills to step in to help. Who cares if they have to endure a bit of teasing along the way?