Everything considered as part of final lesson (2,3)
I believe the answer is:
in all
'everything considered' is the definition.
('in all' can mean taking into account everything)
'part of final lesson' is the wordplay.
'part of' says the answer is hidden in the clue.
'IN ALL' is hidden within 'final lesson'.
'as' is the link.
(Other definitions for in all that I've seen before include "Taken together" , "Everything considered" , "Summarising" , "Taken as a whole" , "Altogether" .)