A student is after an alternative exam (4)
I believe the answer is:
oral
'exam' is the definition.
(spoken academic test)
'a student is after an alternative' is the wordplay.
'student' becomes 'l' (as in L-plates for learner drivers).
'is after' means one lot of letters go next to another.
'an alternative' becomes 'or'.
'a'+'l'='al'
'al' after 'or' is 'ORAL'.
(Other definitions for oral that I've seen before include "'Spoken, not written (4)'" , "Ant; tourist (dial.)" , "from the trap" , "Of the voice" , "Spoken - examination" .)