Bad marks repeatedly in one kind of exam (7)
I believe the answer is:
immoral
'bad' is the definition.
('immoral' can be a synonym of 'bad')
'marks repeatedly in one kind of exam' is the wordplay.
'marks' becomes 'm' (former German currency).
'repeatedly' says to double the letters.
'in' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'kind of exam' becomes 'oral' (I've seen this before).
'm' doubled is 'mm'.
'i'+'oral'='ioral'
'mm' put into 'ioral' is 'IMMORAL'.
(Other definitions for immoral that I've seen before include "Contrary to religious teaching or natural law" , "Corrupt - dissolute" , "dishonest" , "Violating accepted principles of right and wrong" , "Ethically unprincipled" .)