New York City reopened classrooms to many of its youngest students Monday in what has become a frustrating, stop-and-start process in many school systems around the U.S. because of the alarming surge in the coronavirus. .. In contrast, school systems in Detroit, Boston, Indianapolis, Philadelphia and suburban Minneapolis in recent weeks abandoned in-person classes or dropped plans to bring students back because of soaring infections. The retreat in some places and the push forward in others are happening as the virus comes back with a vengeance across much of the U.S…