Boss parts with one of those from school (5)
I believe the answer is:
sprat
'school' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'boss parts with one of those' is the wordplay.
'parts' can be anagrammed to 'SPRAT'.
But, I'm not clear how this is indicated.
'from' acts as a link.
Can you help me to learn more?
(Other definitions for sprat that I've seen before include "Tiny fish" , "Jack, perhaps" , "Traps (anag.)" , "Couple sharing meat" , "Parts of a very small fish" .)