Hate getting low grades on exam (6)
I believe the answer is:
detest
'hate' is the definition.
(to detest is to hate or loathe)
'low grades on exam' is the wordplay.
'low grades' becomes 'de' (D and E are low academic grades).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'exam' becomes 'test' (synonyms).
'de'+'test'='DETEST'
'getting' is the link.
(Other definitions for detest that I've seen before include "Dislike intensely, think badly of" , "Dislike intensely, loathe" , "Abominate" , "Cordially dislike and loathe" , "Not like" .)