The Great Brain, by John D. Fitzgerald, was published in 1967 by Dial.
J. D. idolizes his older brother Tom, a.k.a. the Great Brain, a silver-tongued con man who can turn even the most unlikely situation in to a profitable one. When Papa is the first in town to install indoor plumbing, Tom thinks of a way to make money off of it. When the Jenkins boys get lost in a cave, Tom saves the day—and lines his pockets in the bargain. And when the new teacher paddles him for not being a tattletale, the Great Brain comes up with an ingenious scheme to get rid of the paddle and the teacher.