Don to assess student teacher’s finals with that (3,2)
I believe the answer is:
try on
'don to assess' is the definition.
(don an item of clothing to see if it fits)
'student teacher's finals with that' is the wordplay.
'finals' says to take the final letters (the final letters).
'with' is a charade indicator (letters next to each other).
'that' becomes 'yon' (archaic term meaning 'that').
The last letters of 'student teacher' are 'tr'.
'tr'+'yon'='TRY-ON'
(Other definitions for try on that I've seen before include "audacious imposition" , "Attempt at deception" , "Fitting" , "Test a garment for fit" , "attempted deception" .)