The favourite's in a class by himself (8,3)
I believe the answer is:
teachers pet
'the favourite's in a class by himself' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'the favourite's in a class by himself' is the wordplay.
I cannot quite see how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
'a' is present in the answer.
'himself' could be 'he' (I've seen this in other clues) and 'he' is found within the answer.
'favourite' could be 'pet' (synonyms) and 'pet' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for teachers pet that I've seen before include "(Mocked) school favourite" , "goody-goody" , "Subject of favouritism at school" , "Favoured pupil" , "Class favourite" .)