Call student support, upset (4)
I believe the answer is:
dial
'call' is the definition.
(as in making a phone call)
'student support upset' is the wordplay.
'student' becomes 'L' (as in L-plates for learner drivers).
'support' becomes 'aid' (to aid is to help or support).
'upset' is a reversal indicator.
'l'+'aid'='laid'
'laid' written backwards gives 'DIAL'.
(Other definitions for dial that I've seen before include "Laid up like clock-face" , "Face of a timepiece" , "Clock face" , "Ring the clock-face" , "Watch face" .)