School has ordered window (4)
I believe the answer is:
sash
'window' is the definition.
(I've seen this before)
'school has ordered' is the wordplay.
'school' becomes 'S'.
'ordered' indicates an anagram.
'has' anagrammed gives 'ash'.
's'+'ash'='SASH'
(Other definitions for sash that I've seen before include "Long strip of material - window frame" , "Ribbon as a symbol of rank" , "Item of clothing - frame for glass" , "Framework holding window panes" , "Broad band, the one me father wore?" .)