Restless, always cutting school (8)
I believe the answer is:
feverish
'restless' is the definition.
(thesaurus)
'always cutting school' is the wordplay.
'always' becomes 'ever' (synonyms).
'cutting' means one lot of letters goes inside another (some letters cut their way into a word).
'school' becomes 'fish' (group of fishes).
'ever' going into 'fish' is 'FEVERISH'.
(Other definitions for feverish that I've seen before include "Frenzied" , "Suffering from a high temperature" , "restless state" , "hectic" , "Febrile" .)