Student drops out of study to make money (4)
I believe the answer is:
earn
'make money' is the definition.
(I've seen this before)
'student drops out of study' is the wordplay.
'student' becomes 'l' (as in L-plates for learner drivers).
'drops out of' suggests deleting specific letters.
'study' becomes 'learn' (learning is a kind of studying).
'learn' with 'l' removed is 'EARN'.
'to' acts as a link.
(Other definitions for earn that I've seen before include "Gain through labour or work" , "Merit (a reward)" , "Be paid for work" , "Make; deserve" , "Gain (money, reputation, etc)" .)