Student to gross master (5)
I believe the answer is:
learn
'master' is the definition.
(I've seen this in another clue)
'student to gross' is the wordplay.
'student' becomes 'l' (as in L-plates for learner drivers).
'to gross' becomes 'earn' (I've seen this in another clue).
'l'+'earn'='LEARN'
(Other definitions for learn that I've seen before include "Become aware of" , "Come to know" , "Gain knowledge or skills" , "Renal (anag)" , "Study or digest" .)