Medium Bag Size around 16-18 inches in height, 11-13 inches in width, and 6-7 inches in depth. Should be weighing around 4.5 - 6.8 kg
Implement a “minimalist packing” policy, encouraging teachers to reduce the amount of material students need to carry daily. In my personal experience, children can be taught to share books and a strong school policy should be made to maintain a healthy weight of bag.

Consider Medium to Largensize bag of approximately 18-20+ inches in height, 13-15+ inches in width, and 6-8+ inches in depth. Children should rotate their bags depending on the load of books.
Weight of packed bag should be no more than 15% of the student’s body weight, but realistically, often closer to 15-20 pounds 6.8 - 9 kg
Students in higher classes often have heavier loads due to textbooks, laptops, and extracurricular supplies. Proper ergonomic design and weight distribution are absolutely critical. Consider backpacks with multiple compartments and padded straps/back panels.
Consider digital textbooks or online resources to reduce load.

Weight of school bags is an ongoing discussion but few steps can be taken to reduce this load as such.

Promote Digital Learning: Encourage the use of electronic textbooks and online resources, its not applicable for young students.
Review Bag Contents Regularly: Help children identify unnecessary items, this is the most effective way, children are messy and they overstuff their bags. They like to show off their stationary items, I have found my son carrying coloring pen, A4 sheets and sticky notes for whole class!
Teach Proper Lifting Techniques: Bend at the knees, keep the bag close to the body. Don't let the bag slide down till your glutes, keep the straps tight.
Communication: Open dialogue between parents, teachers, and students about bag weight and comfort. School policies on keeping books and art and craft materials in school.

Blog topic : school supplies

Tips on Buying Right Size School Bag for Kids