Class of Marines sorted out (7)
I believe the answer is:
seminar
'class' is the definition.
(seminar is a kind of class)
'marines sorted out' is the wordplay.
'sorted out' indicates an anagram.
'marines' anagrammed gives 'SEMINAR'.
'of' is the link.
(Other definitions for seminar that I've seen before include "University course" , "Meeting for study" , "Short intensive study course for marines" , "Small discussion group for advanced students" , "Training conference" .)