Cry about student being messy sort (4)
I believe the answer is:
slob
'messy sort' is the definition.
(I've seen this in another clue)
'cry about student' is the wordplay.
'cry' becomes 'sob' (sobbing is a kind of crying).
'about' indicates putting letters inside.
'student' becomes 'l' (as in L-plates for learner drivers).
'sob' placed around 'l' is 'SLOB'.
'being' is the link.
(Other definitions for slob that I've seen before include "Sort of ice" , "Slovenly layabout" , "Couch potato" , "Slovenly and unkempt type" , "Uncouth person" .)