Teacher in a middle school classroom for several years, the blog author is familiar with the challenges of organization for tweens. The tween age span is very subjective. People like to define it as between ages 9 and 12. I include the early teen years, those in the 7th and 8th grade range, as there is still a huge gap in maturity between most of these students and the teen.
While some tweens are a bit more organized, I've rarely encountered one that has it all together when it comes to school bags. On the other hand, there are those that struggle severely with organization. Their school bags are a disaster zone. If they have lockers, the same is true of the locker. They need serious help and oversight. I know. I was that tween.
It's amazing, because I'm still organizationally challenged as an adult. The right tool makes a huge difference. There needs to be space, and it's got to be manageable. I can't stress enough how much I like the use of messenger school bags for tweens. You have to watch the designs you choose for boys, making sure they don't look like purses. Organizationally, the messenger is more like a file. The backpack is subject to dumping stuff in and going. A good alternative for boys is a duffle bag, but recognize that this will be more prone to dumping. It's spacious, though, a nice point.
Keeping gym clothes separate is challenging. In my tween years, we rolled the clothes in our P.E. towels and held them together with rubber bands. When I was in the classroom, my students tended to stuff them in their backpacks. A separate bag, like a sack pack, is a nice way to keep the sweaty sock smell at bay.
Tools for the inside of a bag are helpful. Pencil pouches and binders aid in this endeavor. Tweens and tech gadgets in school bags don't mix well. Protective cases on calculators are a must. Texas Instruments are some of the sturdiest.