Today's youngsters navigate cyberspace like little MIT grads, so it shouldn't be surprising that their art is sophisticated too. Last spring, four art teachers from two Lakewood Middle Schools (Harding and Emerson) selected the best work of their seventh- and eighth-grade students for the schools' second annual exhibit at the Dead Horse Gallery. Fifty students contributed about 150 works, ranging from masks and mobiles to prints and paintings. Leaving representational images of butterflies and Black Beauty in the dust, the youngsters dismantled the picture plane, Picasso-style, and explored art's myriad isms. Much of the work displayed a startling technical and emotional precocity; the most mind-blowing was a cubist portrait of a melancholy young girl with a greenish face and orange hair, staring out of the frame, as if searching for something. The show also taught kids the business side of the art world: Students priced their artwork and made 50 percent on every sale; Dead Horse donated the other half to the schools' art programs.