This musical adaptation of Jerry Spinelli's award-winning novel, presented by New York City Children's Theater, is lots of fun - too much fun for anyone who admires the book's poignant, sometimes disturbing exploration of preadolescent peer pressure. The show, by Rebekah Greer Melocik and Jacob Yandura, finds as much comedy as possible in the struggles of the novel's young hero, Palmer, who opposes his town's annual pigeon shoot, and it replaces Mr. Spinelli's bittersweet ending with a rollicking, upbeat conclusion (1:10).