Boy following college agreement (6)
I believe the answer is:
unison
'agreement' is the definition.
(unison is a kind of agreement)
'boy following college' is the wordplay.
'boy' becomes 'son' ('son' can be a synonym of 'boy'**).
'following' means one lot of letters go next to another.
'college' becomes 'uni' (I've seen this in other clues).
'son' after 'uni' is 'UNISON'.
(Other definitions for unison that I've seen before include "Close agreement" , "Concord; a trade union" , "Concord, sounding or singing together" , "Total agreement or concord" , "Public service trade union" .)