Wear both straps.
Use of one strap causes one side of the body to bear the weight of the backpack. By wearing two shoulder straps, the weight of the backpack is better distributed.

Wear the backpack over the strongest mid-back muscles.
Pay close attention to the way the backpack is positioned on the back. It should rest evenly in the middle of the back. Shoulder straps should be adjusted to allow the child to put on and take off the backpack without difficulty and allow free movement of the arms. Straps should not be too loose, and the backpack should not extend below the low back.

Lighten the load.
Keep the load at 10-15% or less of the child’s bodyweight. Carry only those items that are required for the day. Organize the contents of the backpack by placing the heaviest items closest to the back. Some students have two sets of books so as not to have to carry the heavy books to and from school.