Colleges and small church Oslo rebuilt (7)
I believe the answer is:
schools
'colleges' is the definition.
(I know this)
'small church oslo rebuilt' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'church' becomes 'ch' (common abbreviation).
'rebuilt' is an anagram indicator.
'oslo' anagrammed gives 'ools'.
's'+'ch'+'ools'='SCHOOLS'
'and' acts as a link.
(Other definitions for schools that I've seen before include "Institutions of learning" , "Places of instruction" , "Institutes of learning" , "dolphins in groups, for example" , "Educates" .)