Teacher's pet, last to be expelled (5)
I believe the answer is:
rabbi
'teacher's' is the definition.
(Jewish teacher)
'pet last to be expelled' is the wordplay.
'pet' becomes 'rabbit' (a rabbit might be kept as a pet).
'last' becomes 't' (I've seen this in other clues).
'to be expelled' is a deletion indicator.
'rabbit' with 't' taken away is 'RABBI'.
(Other definitions for rabbi that I've seen before include "Jewish minister" , "Blue" , "Spiritual leader of a Jewish congregation" , "Teacher of Jewish law" , "Minister of a synagogue" .)