Idiot student's breaking point (4)
I believe the answer is:
dolt
'idiot' is the definition.
(I know that idiot can be written as dolt)
'student's breaking point' is the wordplay.
'student' becomes 'l' (as in L-plates for learner drivers).
'breaking' means one lot of letters goes inside another.
'point' becomes 'dot' (synonyms).
'l' placed into 'dot' is 'DOLT'.
(Other definitions for dolt that I've seen before include "Simpleton" , "dope" , "Halfwit" , "Dimwit" , "Idiot" .)