Who is the narrator, can she or he read minds, and, more importantly, can we trust her or him?
First Person (Peripheral)
Youngest Fitzgerald brother J.D. is the narrator, but the subject of his story is the middle brother, Tom, a.k.a. the Great Brain. Generally speaking, the title character is the main character, and that's the case here: J.D. is an active, important character, but he points the lens away from himself and at Tom and his many schemes. Check it out:
My brother very solemnly informed Mr. Kokovinis there were certain things Basil would need, like marbles, to be able to play with other kids, and these things would cost money. Tom generously offered to help Basil get these things. I was bug-eyed as I watched Mr. Kokovinis hand Basil a whole silver dollar. I couldn't help thinking he would have saved time by just giving the dollar to Tom. (5.64)
It's Tom's world; J.D.'s just living in it… and telling readers all about it.