Perhaps school bags always very hot (8)
I believe the answer is:
feverish
'very hot' is the definition.
'perhaps school bags always' is the wordplay.
'perhaps school' becomes 'fish' (school can mean a group of fish).
'bags' indicates putting letters inside (bag can mean secures or steals).
'always' becomes 'ever' (synonyms).
'fish' placed around 'ever' is 'FEVERISH'.
(Other definitions for feverish that I've seen before include "Extremely excited" , "Restless with excitement or agitation - got ague?" , "Restlessly excited" , "Suffering from a high temperature" , "restless state" .)