Bag for school books (7)
I believe the answer is:
satchel
'bag for school books' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for satchel that I've seen before include "Bag with a flap and strap" , "Shoulder bag as for schoolbooks" , "Carrier for school books" , "Get school item" , "Schoolchild's carrier" .)