To date he'd moved student taken in by promise to be out (4,2,3,5)
I believe the answer is:
dead to the world
'be out' is the definition.
(knocked out)
'to date he'd moved student taken in by promise' is the wordplay.
'moved' indicates an anagram.
'student' becomes 'l' (as in L-plates for learner drivers).
'taken in by' is an insertion indicator.
'promise' becomes 'word' (as in 'I give you my word').
'l' going within 'word' is 'world'.
'to'+'date'+'hed'='todatehed'
'todatehed' is an anagram of 'deadtothe'.
'deadtothe'+'world'='DEAD TO THE WORLD'
'to' acts as a link.
(Other definitions for dead to the world that I've seen before include "Fast asleep" , "Sound asleep; unconscious" , "Sleeping" .)