Make progress, starting Greek at school (3,2)
I believe the answer is:
get on
'make progress' is the definition.
(synonyms)
'starting greek at school' is the wordplay.
'starting' suggests taking the first letters.
'at' says to put letters next to each other.
'school' becomes 'eton' (famous UK public school).
The first letter of 'greek' is 'g'.
'g'+'eton'='GET ON'
(Other definitions for get on that I've seen before include "Age; prosper" , "Board (a bus)" , "Make progress; be friends" , "fare" , "Make progress or advance in age" .)