Finishes off boring school soup (6)
I believe the answer is:
borsch
'soup' is the definition.
(I know that Borsch is a type of soup)
'finishes off boring school' is the wordplay.
I cannot really understand how this works, but
'school' could be 'sch' (abbreviation) and 'sch' is found in the answer.
The remaining letters 'bor' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for borsch that I've seen before include "Russian or Polish soup usually containing beet juice" , "Russian beetroot soup" , "Soup made with beetroot" .)