Fish out a key to the school, girl! (2-2)
I believe the answer is:
co-ed
'the school girl' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'fish out a key' is the wordplay.
'fish' becomes 'cod' (cod is a kind of fish).
'out' is an insertion indicator.
'a key' becomes 'e' (I've seen this in other clues).
'cod' placed around 'e' is 'CO-ED'.
'to' is the link.
Can you help me to learn more?
(Other definitions for co-ed that I've seen before include "Teaching attended by both sexes" , "Teaching both girls and boys" , "School for both sexes" , "School for boys and girls, in short" .)