Teacher locked up, being wasted (8)
I believe the answer is:
misspent
'being wasted' is the definition.
(thesaurus)
'teacher locked up' is the wordplay.
'teacher' becomes 'miss' (I've seen this before).
'locked up' becomes 'pent' (I've seen this in other clues).
'miss'+'pent'='MISSPENT'
(Other definitions for misspent that I've seen before include "Wasted (as youth)" , "Like many a youth" , "youth? Sort of" , "troublesome youth?" , "having used money unwisely" .)