Pupil's joint academic achievement (11)
I believe the answer is:
scholarship
'academic achievement' is the definition.
(I've seen this before)
'pupil's joint' is the wordplay.
'pupil's' becomes 'scholars' (scholar is a kind of pupil**).
'joint' becomes 'hip' (hip is a kind of joint).
'scholars'+'hip'='SCHOLARSHIP'
(Other definitions for scholarship that I've seen before include "Work of 6 [ACADEMIA]" , "Educational grant" , "(Award for) academic skill" , "Academic achievement" , "Student maintenance grant" .)