Prosper in good school (3,2)
I believe the answer is:
get on
'prosper' is the definition.
(I've seen this before)
'good school' is the wordplay.
'good' becomes 'g' (abbreviation).
'school' becomes 'eton' (famous UK public school).
'g'+'eton'='GET ON'
'in' is the link.
(Other definitions for get on that I've seen before include "Make progress or climb aboard" , "Enjoy harmonious relationship" , "Make progress; be friends" , "fare" , "Obtain promotion" .)