(Washington Post) — The two Southeast Washington middle schools are less than a mile apart. The real distance that separates them is the number of hours their students spend in class each week. At Johnson Middle School, the day is 61/2 hours, 8:45 a.m. to 3:15 p.m. Students at AIM Academy, a KIPP charter school, stay for nine hours, from 8 a.m. to 5 p.m. Monday through Thursday, and 71/2 hours on Friday. That doesn’t count the mandatory 15 days of summer school and numerous four-hour Saturday sessions. In all, AIM kids spend 40 percent more time in class than their D.C. public school peers. Longer school days are expensive and complicated to execute, requiring buy-in from teachers, parents, after-school programs and child-care providers. And the evidence that extended schedules actually improve academic performance is mixed at best.