Complete agreement college needs boy to follow (6)
I believe the answer is:
unison
'complete agreement' is the definition.
(unison can mean total agreement or harmony)
'college needs boy to follow' is the wordplay.
I cannot really understand how this works, but
'college' could be 'uni' (short for university) and 'uni' is present in the answer.
'boy' could be 'son' (synonyms) and 'son' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for unison that I've seen before include "Accord" , "Type of singing" , "Sameness in pitch" , "Agreement or concord, as with choir" , "Total agreement or concord" .)