Most school systems follow a formula, choosing to shut down when student absenteeism reaches a certain level, said Tom Ferguson, assistant superintendent of schools in Shelby County, Ala.

• 阿拉巴马州谢尔比县学校助理监督弗格森汤姆说，大多数学校系统遵循这样的一个模式：学生旷课达到一定水平时，选择关闭。