Dressed as college boy (4)
I believe the answer is:
clad
'dressed' is the definition.
(to be clad in something is to be dressed in it)
'college boy' is the wordplay.
'college' becomes 'c'.
'boy' becomes 'lad' (informal term for boy).
'c'+'lad'='CLAD'
'as' is the link.
(Other definitions for clad that I've seen before include "Clothed, covered" , "Invested" , "Decked" , "Cover with insulation" , "Wearing" .)