North Chevy Chase Elementary School, with a demanding curriculum, strong faculty and high student test scores, meets nobody's definition of a failure. Nobody's, that is, except the federal government's.Last year, the Montgomery County school failed to make what the government calls "adequate yearly progress," even though 91 percent of its students passed the state math test and 96 percent passed in reading. The school fell short for the first time because a handful of students with disabilities missed the target in math.Confusion over the ratings of schools such as this one and thousands of others nationwide is fueling President Obama's drive to rewrite the nine-year-old No Child Left Behind law. In his State of the Union Address on Tuesday, Obama called for a version that is "more flexible...