In-form favourite confuses respect with hate (8,3)
I believe the answer is:
'in-form favourite' is the definition.
(form can mean a school class)
'confuses respect with hate' is the wordplay.
'confuses' indicates an anagram.
'with' says to put letters next to each other.
'respect' after 'hate' is 'haterespect'.
'haterespect' is an anagram of 'TEACHERS PET'.
(Other definitions for teachers pet that I've seen before include "Subject of favouritism at school", "Student of form favoured", "(Mocked) school favourite", "Favourite in form", "Favoured child at school".)