The Young Tars — Eric Kraft

Peter Leroy recalls an episode from his grade-school years, an episode that he would really rather forget, one of the dark, gritty bits that one finds at the bottom of the chowder bowl of life. It involves the Young Tars, an organization originally intended to raise the morale of students at the new Babbington Central Upper Elementary School, and the treacherous Mr. Summers, a teacher whose armamentarium of instructional techniques featured "humility sessions" and a toy weapon that fired ping-pong balls.
Reviewing the original edition of the novellas that became Little Follies, Lee Pennock Huntington wrote, in the Vermont Sunday Magazine:

Peter is a thoroughly likable lad. He is bright and observant, but also subject to all the anxieties and misapprehensions of childhood. His parents, grandparents, neighbors, classmates, teachers, and friends are all marvelously alive, individual, eccentric. What happens to them has all the elements of surprise and inevitability that characterize the human condition, and some of it is so funny you can scarcely turn the pages for chortling. But in presenting his characters in all their banality, looniness, and bungling, Kraft does it with a kind of tender respect for the basic dignity of even the most pathetic and obnoxious.

Length: novella, about 20,000 words; about 96 pages in a trade paperback edition