NEW YORK — When the Associated Press set out to investigate an apparent problem with sexual assault of children in public schools, the organization spared no expense. A congressionally mandated study by Hofstra University had already found school-based sexual abuse to be a big problem. “It was one of our priorities for the year,” said John Affleck, editor of the AP’s national reporting team.The result was a three-part series, available to editors throughout the country beginning Oct. 20, that revealed widespread and routine sexual assault of public school students throughout the country. The first story summarized: “Students in America’s schools...