Dear Lucia 13,
A �Locker� is a small personal cupboard, which has a key to lock it. You see lockers at the Swimming Baths; the Sports Centre; (to store the customers� clothes); and sometimes in schools, colleges, etc. (so that students can store books, etc). The person has the key to his/her locker.
If the students had lockers, in the classroom, or in the corridor, I would say:
"Put your books away in your Locker (Lockers), please!"
or, if the students had desks which opened and had storage space inside:
"Put your books away in your (Desk) Desks, please!"
or simply:
"Put your books away, please!"
I hope that this helps.
Les