Pupil producing rubbish say in exercise (7)
I believe the answer is:
protege
'pupil' is the definition.
(I know that protege is a type of pupil)
'rubbish say in exercise' is the wordplay.
'rubbish' becomes 'rot' (both can mean nonsense).
'say' becomes 'eg' (both can mean 'for example').
'in' indicates putting letters inside.
'exercise' becomes 'pe' (Physical Education).
'rot'+'eg'='roteg'
'roteg' put into 'pe' is 'PROTEGE'.
'producing' is the link.
(Other definitions for protege that I've seen before include "One guided and supported by another" , "One taken under someone's wing" , "One under another's patronage" , "One under the patronage of another" , "A protected species" .)