Residents of the District and their elected leaders have long agonized over the state of D.C. schools, a third rail in Washington city government off of which reform attempts gleefully bounce and into which depressing sums of money disappear. Frustration over the city’s subpar performance in public education becomes more difficult to bear, however, when the success of school districts in the city’s suburbs are brought to light. This week, the Post’s Jay Mathews harnesses…