Remain outside school control (9)
I believe the answer is:
restraint
'control' is the definition.
(restraint is a kind of control)
'remain outside school' is the wordplay.
'remain' becomes 'rest' ('rest' can be a synonym of 'remain').
'outside' indicates putting letters inside.
'school' becomes 'train' (training is a kind of schooling**).
'rest' enclosing 'train' is 'RESTRAINT'.
(Other definitions for restraint that I've seen before include "Limiting device" , "Start rain as an impediment" , "Moderation" , "It keeps someone or something under control" , "Reserve" .)