CHATTANOOGA, Tenn. (AP) — An ex-Tennessee school bus driver who was at the wheel in a wreck that killed six children has been sentenced to four years in prison for criminally negligent homicide. Media reported that a Chattanooga judge sentenced Johnthony Walker on Tuesday after an emotional morning of testimony, during which Walker apologized. Judge Don Poole ruled Walker shouldn't be sentenced to diversion because the crash involving 37 elementary school students was so horrific, but he couldn't give him a longer prison term because of his strong work history and no criminal background.