One's scored highly against test upon leaving institute (9)
I believe the answer is:
contralto
'leaving institute' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'one's scored highly against test' is the wordplay.
I cannot really understand how this works, but
'against' could be 'contra' (I've seen this before) and 'contra' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'upon' acts as a link.
Can you help me to learn more?
(Other definitions for contralto that I've seen before include "Lowest female singing voice" , "Total corn! (anag)" , "Female voice of the lower register." , "deep, for women" , "Lowest female singer" .)