Student group starts to improve and creates great work (7)
I believe the answer is:
classic
'great work' is the definition.
(eg a literary classic)
'student group starts to improve and creates' is the wordplay.
'student group' becomes 'class' (eg a class at school).
'starts to' says to take the initial letters.
'and' says to put letters next to each other.
'creates' becomes 'c' (this could be a standard abbreviation of which I'm unaware).
The first letter of 'improve' is 'i'.
'class'+'i'+'c'='CLASSIC'
(Other definitions for classic that I've seen before include "Epsom Derby or St Leger Stakes, for example" , "Definitive; of recognised excellence" , "Top-quality" , "Derby, say" , "The best of its kind" .)