Jack Finch, principal at Chesapeake Elementary School in Lawrence County, Ohio, has weighed students� backpacks, he said. One little girl who weighed 40 pounds had to lean forward to manage her 26-pound backpack.
This is a great article, even though there is a comment by a chiropractor (charlatan!). It is unfathomable that kids have to carry books for all of their classes because there is not enough time to go to their lockers. There is also a list of what you can do to improve the situation from the American Academy of Orthopedic Surgeons.
Lower back pain is supposed to be for us old folks, not kids.
I have found it helpful to do the stretching exercises my physical therapist recommends. Do some core strengthening exercises, such as the ones highlighted at The Mayo Clinic. By keeping your core strong, your back won't put itself in a position to cause that sciatica pain you are having.