Students of French enthralled by derrières (7)
I believe the answer is:
readers
'students' is the definition.
(reader is a kind of student)
'of french enthralled by derrieres' is the wordplay.
'of french' becomes 'de' ('of' in French).
'enthralled by' is an insertion indicator ('enthral' can mean 'capture').
'derrieres' becomes 'rears' ('rear' can be a synonym of 'derriere').
'de' inserted within 'rears' is 'READERS'.
(Other definitions for readers that I've seen before include "Senior lecturers" , "cheaters" , "Lectors" , "bookworms" , "Student textbooks" .)