Grab and beat up in school (6)
I believe the answer is:
snatch
'grab' is the definition.
('snatch' can be a synonym of 'grab')
'beat up in school' is the wordplay.
'beat' becomes 'tan' (I've seen this before**).
'up' is a reversal indicator (in down clue: letters go upwards).
'in' is an insertion indicator.
'school' becomes 'sch'.
'tan' reversed gives 'nat'.
'nat' inserted inside 'sch' is 'SNATCH'.
'and' acts as a link.
(Other definitions for snatch that I've seen before include "Bit of a song" , "Sieze or grab" , "Dense clump of grass" , "Seize quickly, grab" , "E. Mediterranean nation" .)