Believe this is good exam grade (6)
I believe the answer is:
credit
This clue might be a double definition.
'believe' is the first definition.
(I've seen this in another clue)
'good exam grade' is the second definition.
'credit' can be an answer for 'grade' (I have seen 'good grade' mean 'credit' so perhaps 'grade' could also mean 'credit'). I'm not sure about the 'good exam' bit.
'this is' is the link.
Can you help me to learn more?
(Other definitions for credit that I've seen before include "entry in cashbook" , "Tick - distinction" , "Have faith" , "good grade" , "Arrangement for deferred payment" .)