Pulls hardworking student up ... (4)
I believe the answer is:
tows
'pulls' is the definition.
(I know this)
'student up' is the wordplay.
'student' becomes 'swot' (I have seen 'diligent student' mean 'swot' so perhaps 'student' could also mean 'swot').
'up' is a reversal indicator (in down clue: letters go upwards).
'swot' reversed gives 'TOWS'.
'hardworking' is the link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for tows that I've seen before include "Tugs" , "Pulls" .)