Beating the Bounds
On Holy Thursday, or Ascension Day, it used to be customary for the parish school children, accompanied by the clergymen and parish officers, to walk through their parish from end to end. The boys were struck with willow wands all along the lines of boundary. Before maps were common, the boys were thus taught to know the bounds of their own parish. The custom still prevails in some parishes.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894