Go off, taking girlfriend around school (8)
I believe the answer is:
detonate
'go off' is the definition.
(thesaurus)
'girlfriend around school' is the wordplay.
'girlfriend' becomes 'date' (I've seen this in other clues).
'around' means one lot of letters goes inside another.
'school' becomes 'eton' (famous UK public school).
'date' enclosing 'eton' is 'DETONATE'.
'taking' is the link.
(Other definitions for detonate that I've seen before include "Start 15 [EXPLOSION]" , "Discharge" , "Blow up, explode" , "let off" , "Set off explosive device" .)