A rare and working Treen ‘clicker’ and a fabulous piece of social history.
These devices were used by school teachers to caution or reprimand wayward students . I suppose it’s better than getting a rap on the knuckles with a ruler ! Perhaps they were also used to meter rote learning such as times tables . 
As detailed in the Treen ‘bible’ by Edward Pinto. This particular one is an early example and it would have  had the gut stringing as opposed to a later spring mechanism. C1820.