Creep dropping behind student brainbox? (5)
I believe the answer is:
skull
'brainbox?' is the definition.
(I've seen this before)
'creep dropping behind student' is the wordplay.
'creep' becomes 'skulk' (both can mean to move around furtively).
'dropping behind' means to remove the last letter (the word's back or behind is dropped).
'student' becomes 'l' (as in L-plates for learner drivers).
'skulk' with its last letter removed is 'skul'.
'skul'+'l'='SKULL'
(Other definitions for skull that I've seen before include "Bony part of head" , "brains here" , "Brain casing" , "Pirate flag feature" , "Brainbox" .)