Divorce and its effect on children is a topic movies have worked to death. Writer- director Noah Baumbach (Kicking and Screaming, Mr. Jealousy) discovers it fresh and with fierce insight and feeling in a movie where even the laughs cut to the bone. Baumbach sets the film in Brooklyn’s Park Slope, where he lived in the 1980s during and after the breakup of his own parents, former film critic Georgia Brown and novelist Jonathan Baumbach. In the film, Jeff Daniels plays Bernard, the academic dad in career crisis, with the vividly scrappy Laura Linney as Joan, the wife whose writing is just beginning to be recognized. Jesse Eisenberg, so good in Roger Dodger, amazes again as sixteen-year-old Walt, Baumbach’s surrogate. And Owen Kline — son of actors Kevin Kline and Phoebe Cates — is a marvel as Frank, a twelve-year-old for whom jerking off has become a vocation. The boys react in different ways to their overachieving parents, especially when Mom screws the tennis pro (William Baldwin), and Dad’s student (Anna Paquin) moves in with him. At school, Walt passes off Pink Floyd’s “Hey You” as his own, and Frank finds ever-more-intriguing places to dispose of his jism. All the performances are flawless, but Daniels’ portrait of a man trying helplessly to break out of the cocoon of his own self-regard is a finely tuned tour de force and his shining hour onscreen. Without jerking tears or reducing the acid content of his wit, Baumbach’s humane movie gets under your skin.