Unaffected by a turn performed by a student (7)
I believe the answer is:
natural
'unaffected' is the definition.
(similar in meaning)
'a turn performed by a student' is the wordplay.
'performed' indicates anagramming the letters.
'by' means one lot of letters go next to another.
'student' becomes 'l' (as in L-plates for learner drivers).
'a'+'turn'='aturn'
'aturn' is an anagram of 'natur'.
'natur'+'a'+'l'='NATURAL'
'by' acts as a link.
(Other definitions for natural that I've seen before include "One regarded as sure to succeed in some field" , "spontaneous" , "(Of fabric) off-white" , "sort of history" , "Frank < , twenty-one" .)