A turn performed by a student is unaffected (7)
I believe the answer is:
natural
'unaffected' is the definition.
(similar in meaning)
'a turn performed by a student' is the wordplay.
'performed' is an anagram indicator.
'by' is a charade indicator (letters next to each other).
'student' becomes 'l' (as in L-plates for learner drivers).
'a'+'turn'='aturn'
'aturn' is an anagram of 'natur'.
'natur'+'a'+'l'='NATURAL'
'is' is the link.
(Other definitions for natural that I've seen before include "character on the staff" , "pure" , "Certainty" , "Ordinary" , "Normal - genuine" .)