Remains with teacher carrying mattress upstairs (6)
I believe the answer is:
debris
'remains' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for debris that I've seen before include "'Ruins, rubble (6)'" , "Refuse, litter" , "Remains - wreckage" , "Refuse remains" , "Brides with pieces of rubble" .)