Heard residential pupils in beds (7)
I believe the answer is:
borders
'beds' is the definition.
(flower beds)
'heard residential pupils' is the wordplay.
'heard' indicates a 'sounds like' (homophone) clue.
'residential pupils' becomes 'boarders' (boarding school pupils).
'boarders' is a homophone of 'BORDERS'.
'in' acts as a link.
(Other definitions for borders that I've seen before include "Decorative edges" , "Boundary lines" , "Perimeters" .)