Green art evolved first sort of nursery (12)
I believe the answer is:
kindergarten
'nursery' is the definition.
(I've seen this before)
'green art evolved first sort' is the wordplay.
'evolved' indicates anagramming the letters (the order of letters changes or evolves).
'first' is a charade indicator (letters next to each other).
'sort' becomes 'kind' (synonyms).
'green'+'art'='greenart'
'greenart' anagrammed gives 'ergarten'.
'ergarten' after 'kind' is 'KINDERGARTEN'.
'of' acts as a link.
(Other definitions for kindergarten that I've seen before include "Hamburger's first class" , "Infant school" , "Pre-school class" , "Where master may be" , "Nursery school" .)