Teacher’s disapproving expression: nothing right! (5)
I believe the answer is:
tutor
'teacher's' is the definition.
(tutor is a kind of teacher)
'disapproving expression nothing right' is the wordplay.
'disapproving expression' becomes 'tut' (tut tut!).
'nothing' becomes 'O' (looks like zero - 0).
'right' becomes 'r' (abbreviation).
'tut'+'o'+'r'='TUTOR'
(Other definitions for tutor that I've seen before include "train" , "Individual teacher" , "Private educator" , "Master" , "Private instructor" .)