Trying experience of boy turning up during exam (6)
I believe the answer is:
ordeal
'trying experience' is the definition.
(I've seen this before)
'boy turning up during exam' is the wordplay.
'boy' becomes 'ed'.
'turning up' says the letters should be written backwards.
'during' indicates putting letters inside.
'exam' becomes 'oral' (oral exam is a kind of exam).
'ed' in reverse letter order is 'de'.
'de' put into 'oral' is 'ORDEAL'.
'of' acts as a link.
(Other definitions for ordeal that I've seen before include "Struggle" , "Horrific experience" , "A difficult and harrowing experience" , "Difficult and testing experience" , "trying affair" .)