The street-filling marches and police clashes get all the attention, but St. Louis students have also begun protesting at their schools following the acquittal of an ex-cop charged with murder.Students in at least three metro high schools, a junior high and universities have staged walkouts or demonstrations since Friday, when Judge Timothy Wilson delivered a not-guilty verdict in the trial of Jason Stockley. The former St. Louis police officer fatally shot Anthony Lamar Smith in 2011 following a high-speed chase in north city.…