Demanding rest fuss about student (9)
I believe the answer is:
stressful
'demanding' is the definition.
'rest fuss about student' is the wordplay.
'about' is an anagram indicator.
'student' becomes 'L' (as in L-plates for learner drivers).
'rest'+'fuss'='restfuss'
'restfuss' anagrammed gives 'stressfu'.
'stressfu'+'l'='STRESSFUL'
(Other definitions for stressful that I've seen before include "Creating tension" , "Causing mental tension" , "tense" , "Worrying" , "under great pressure" .)