Express disapproval over one interrupting examination class (8)
I believe the answer is:
tutorial
'class' is the definition.
(I've seen this before)
'express disapproval over one interrupting examination' is the wordplay.
'express disapproval over' becomes 'tut' (I've seen this in other clues).
'one' becomes 'i' (Roman numeral).
'interrupting' is an insertion indicator.
'examination' becomes 'oral' (oral is a kind of examination).
'i' inserted into 'oral' is 'orial'.
'tut'+'orial'='TUTORIAL'
(Other definitions for tutorial that I've seen before include "University study period" , "Period of individual instruction" , "Session of intensive teaching to an individual or small group" , "Private lesson" , "Rail tout (anag)" .)