The four criteria for assessing class importance apply to clapper bridge as follows:
- Period (currency): Long-lived. It is thought that clapper bridges were mainly built and used between 1400 and the late 18th century or 19th century.
- Rarity: Rare. Only around 40 examples of clapper bridges have been identified at present but many more are likely to have existed during the medieval and early post-medieval periods.
- Diversity (form): Low. Only two types of clapper bridge have been identified.
- Period (representivity): Low. Clapper bridge represent one of a large number of monuments characteristic of the medieval and post-medieval periods.
Assigning scores to these criteria following the system set out in the Monument Evaluation Manual, clapper bridges yield a Class Importance Value of 27. This lies about two-fifths of the way up the range of possible values (max. = 64), reflecting the rarity of the class and its long currency of use. Examples representing both types of clapper bridge and of varying dates should be included in the sample of nationally important sites.