Alternatively a student exam (4)
I believe the answer is:
oral
'exam' is the definition.
(spoken academic test)
'alternatively a student' is the wordplay.
'alternatively' becomes 'or'.
'student' becomes 'l' (as in L-plates for learner drivers).
'or'+'a'+'l'='ORAL'
(Other definitions for oral that I've seen before include "Type of examination" , "Spoken test" , "By word of mouth (4)" , "Mouth-related" , "Spoken rather than written" .)