Cries from characters in trouble at school (6)
I believe the answer is:
bleats
'cries' is the definition.
(bleat is a kind of cry)
'characters in trouble at school' is the wordplay.
'characters in' indicates a hidden word.
'BLEATS' is hidden within 'trouble at school'.
'from' is the link.
(Other definitions for bleats that I've seen before include "The cries of a calf or goat" , "Stable (anag) - pastoral sounds" , "Makes sheep sounds in stable" , "Makes sound like sheep in stable" , "Sheep's cries" .)