Classmate ultimately failing to pass (6)
I believe the answer is:
elapse
'pass' is the definition.
(I know that pass can be written as elapse)
'classmate ultimately failing' is the wordplay.
'ultimately' suggests the final letters.
'failing' becomes 'lapse' (a moral failing).
The last letter of 'classmate' is 'e'.
'e'+'lapse'='ELAPSE'
'to' acts as a link.
(Other definitions for elapse that I've seen before include "Slip away" , "Of time, pass by - please" , "Please (anag) -- pass away" , "Pass or expire - please" , "Passing" .)