Across Atlanta Public Schools, staff worked feverishly in secret to transform testing failures into successes.Teachers and principals erased and corrected mistakes on students’ answer sheets.Area superintendents silenced whistle-blowers and rewarded subordinates who met academic goals by any means possible.Superintendent Beverly Hall and her top aides ignored, buried, destroyed or altered complaints about misconduct, claimed ignorance of wrongdoing and accused naysayers of failing to believe in poor children’s ability to learn.For years — as long as a decade — this was how the Atlanta school district produced gains on state curriculum tests. The scores soared so dramatically they brought national acclaim...