City school sources entrants who are upwardly mobile (4)
I believe the answer is:
oslo
'city' is the definition.
(capital of Norway)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for oslo that I've seen before include "Nordic city" , "Capital city, called Kristiania until 1924" , "Norwegian city, formerly Kristiania" , "foreign port" , "Capital often frozen" .)