Consider sit-com's ability to trivialize. After two decades of inexorable social enlightenment, the Brooklyn Sweathogs have substituted infantile pranks for the switchblade rock of [Richard Brooks's] The Blackboard Jungle, a classroom that has, incidentally, graduated at least three actor-directors in Paul Mazursky, Vic Morrow, and Sidney Poitier. The last, Poitier, seems particularly comfortable in the classroom. The Blackboard Jungle gave him a start; [James Clavell's] To Sir, With Love was a boost at mid-career; and now some of the strongest moments of his several directions appear in A Piece of the Action, in which he allows a younger generation, fresh faces in a ghetto class, their pause in the melodramatic limelight. Poitier's film, which inserts an ode to classroom reform within a caper story, is much too long and no model of neat construction. But in going for that old liberal uplift of A Man Ten Feet Tall...