Pittsburgh police this morning arrested a 14-year-old boy on charges he raped a 14-year-old girl at a North Side city school. The boy, whose name was not released, is accused of grabbing the girl by the arm, throwing her down a set of stairs and assaulting her in the basement of Pittsburgh King, a pre-K-8 school, as the school day ended about 3 p.m. Friday. Police arrested him at school today.