Under national scrutiny after a number of recent arrests of teachers and aides, the chancellor of the New York City public schools, Dennis Walcott, has ordered a review of cases of teacher misconduct. But his direction parallels yet another teacher’s arrest and for many is too little, too late. This week’s arrest saw Reserve Officers Training Corps teacher Darryl Lynch, a teacher at Manhattan’s High School of Graphic Communication Arts, taken from school and charged with sexually touching a 14-year-old female student. Mr. Lynch worked at the school since 1997.