Demolished school by the sound of it (5)
I believe the answer is:
eaten
'demolished' is the definition.
(I've seen this before)
'school by the sound of it' is the wordplay.
'school' becomes 'eton' (famous UK public school).
'by the sound of it' indicates a 'sounds like' (homophone) clue.
'eton' is a homophone of 'EATEN'.
(Other definitions for eaten that I've seen before include "absorbed in the system" , "Got" , "worried" , "Polished off" , "corroded" .)