Perfect score, often (3)
I believe the answer is:
ten
'perfect score often' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ten that I've seen before include "No of sides of a decagon" , "Dudley Moore/Bo Derek film" , "honour" , "Half a score" , "PM's address, Downing St" .)