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How to choose a school bag
Consider your needs.
Take a look at your school's supply list (if they provide you one) and its policies on bags, the textbooks you will be receiving from your school, and whether you'll be using a laptop (mostly in late high school). These factors affect the type and size of the bag you will need.
First of all, see what your school's rules or handbook have to say about backpacks. Certain schools do not allow rolling backpacks or messenger bags, for example, and some have specifications with regards to style or color.