HOW TO START A CEASE-FIRE: LEARNING FROM BOSTON

It is nine o'clock on a gamy summer night, and Bill Stewart is on curfew patrol. The probation officer bounds up the stairs of a Dorchester triple-decker apartment building to check on a boy who was once caught with marijuana. The boy must be home between the hours of 7 p.m. and 7 a.m., seven days a week, under a system of court-ordered curfews for young offenders, each curfew set individually by a judge. There had been worrisome signs of gang involvement in this case. A week ago, someone fired a shotgun blast into the second-floor porch, and the boy's parents...