A six-year-old northern Iowa boy is dead after being struck Tuesday by the school bus that just dropped him off after school. Rudd-Rockford-Marble Rock first grader Derick Wharton was hit by the bus ataround 3:50 yesterday afternoon after being dropped off at the bus stop.Wharton was taken to Floyd County Memorial Hospital in Charles City where hewas pronounced dead. The driver of the school bus, 58-year-old RonaldNavratil, at this time has not been charged.