Disgraceful event in examination -- boy shown up (7)
I believe the answer is:
scandal
'disgraceful event' is the definition.
(I've seen this before)
'examination boy shown up' is the wordplay.
'examination' becomes 'scan' (scan is a kind of examination).
'boy' becomes 'lad' (informal term for boy).
'shown up' says the letters should be written backwards.
'lad' backwards is 'dal'.
'scan'+'dal'='SCANDAL'
'in' acts as a link.
(Other definitions for scandal that I've seen before include "something injurious to one's reputation" , "Malicious gossip" , "Event causing public outrage" , "Subject of Sheridan's school" , "Something shameful or disgraceful, often public" .)