Mark turning to Nick for school folder? (4,6)
I believe the answer is:
eton collar
'school folder?' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'mark turning to nick for' is the wordplay.
'mark' becomes 'note' ('note' can be a synonym of 'mark').
'turning' says the letters should be written in reverse.
'to nick for' becomes 'collar' (I can't explain this - if you can you should give a lot more credence to this answer).
'note' written backwards gives 'eton'.
'eton'+'collar'='ETON COLLAR'
Can you help me to learn more?
(Other definitions for eton collar that I've seen before include "One would ring schoolboy" , "one assumed at school?" .)