Sort-of-linked to The Girl Who Knew It All, Which was sort-of-linked to Fourth Grade Celebrity, this hasn't even the scattiness and frenetic TV tempo of its predecessors to commend it. ""Didn't you know there's no such thing as a left-handed shortstop?"" asks despairing Walter Moles' father a third of the way through. Science buff Walter, pressed into filling an empty slot on the fourth-grade team, didn't know it of course; and he doesn't want to show up team-captain Gunther--who obviously didn't know it either--by pointing out same. So he contrives with friend Casey Valentine (much more subdued here than in The Girl Who Knew It All) to pretend a disabling broken arm by constructing a papier-mÃ¢chÃ‰ cast. . . which cracks and starts to crumble when gabby friend J.R. insists on autographing it (as any kid might have predicted someone would want to do). But J.R. doesn't give Walter away, and it dawns on Walter that J.R., a baseball nut, also knew there was no such thing as a left-handed shortstop. So he arranges to switch with J.R. in left field, and the fourth-graders beat the fifth-graders--thus winning new-teacher Mr. Dengle's prize of homework-free Fridays. If you're wondering about that prize, it's because Mr. D. is fat, fatuous, and foolish. It's also a device to touch off Walter's troubles. The whole thing is as friable as the papier-mÃ¢chÃ‰, in short, and not particularly funny.