Perceive school's over (4)
I believe the answer is:
note
'perceive' is the definition.
(I've seen this in another clue)
'school's over' is the wordplay.
'school' becomes 'eton' (famous UK public school).
'over' says the letters should be written in reverse.
'eton' back-to-front is 'NOTE'.
(Other definitions for note that I've seen before include "A flat, for example" , "register" , "Crotchet or minim, perhaps" , "Record - piece of music" , "Tenner, for example" .)