Abduction of the Children

Clay was giving a history test to his elementary school students when he noticed talking going on.  He figured that some students were cheating so looked up from a paper he was examining.  He was puzzled to find that most of the boys were missing.  The only one left was a boy with a broken leg.  He was concerned that they may have snuck out so they didn't have to take the test.  So he went out in the hall and found other teachers milling around since they had lost most of their young boys too.  Soon he heard cop cars in the distance and knew something serious had happened to the boys.  The Principal must have panicked and called the police.
This is a science fiction story.