Teacher avoiding extremes, describing artist's pain (7)
I believe the answer is:
earache
'pain' is the definition.
(earache is a kind of pain)
'teacher avoiding extremes describing artist's' is the wordplay.
'avoiding extremes' means to look at the middle letters (letters at the extremes of the word are removed).
'describing' means one lot of letters goes inside another (describe can mean to form the outline of).
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
The middle letters of 'teacher' are 'eache'.
'eache' enclosing 'ra' is 'EARACHE'.
(Other definitions for earache that I've seen before include "Each era (anag)" , "Otalgia" , "Incessant complaining" , "Ace hare (anag.)" , "a problem for some listeners" .)