Refuse society girl and knock back teacher (6)
I believe the answer is:
debris
'refuse' is the definition.
(both can mean rubbish)
'society girl and knock back teacher' is the wordplay.
'society girl' becomes 'deb' (I've seen this in another clue).
'and' says to put letters next to each other.
'knock back' says the letters should be written backwards.
'teacher' becomes 'sir' (way of addressing a male teacher).
'sir' in reverse letter order is 'ris'.
'deb'+'ris'='DEBRIS'
(Other definitions for debris that I've seen before include "Rebids for rubble" , "Fragments of wreckage" , "Broken remains" , "Rubble as of fallen building" , "'Ruins, rubble (6)'" .)