Hate exam following low grades (6)
I believe the answer is:
detest
'hate' is the definition.
(to detest is to hate or loathe)
'exam following low grades' is the wordplay.
'exam' becomes 'test' (synonyms).
'following' says to put letters next to each other.
'low grades' becomes 'de' (I've seen this in other clues).
'test' put after 'de' is 'DETEST'.
(Other definitions for detest that I've seen before include "Dislike heartily" , "Really dislike" , "Cordially dislike and loathe" , "Having a loathing" , "Deplore" .)